Prepreg, method for manufacturing prepreg, substrate, and semiconductor device

ABSTRACT

A prepreg which can meet a demand for thickness reduction is provided. The prepreg has first and second resin layers having different applications, functions, capabilities, or properties, and allows an amount of a resin composition in each of the first and second resin layers to be set appropriately depending on a circuit wiring portion to be embedded into the second resin layer. Further, a method for manufacturing the above prepreg, and a substrate and a semiconductor device having the prepreg are also provided. The prepreg according to the present invention includes a core layer including a sheet-shaped base member and having one surface and the other surface which is opposite to the one surface, the first resin layer provided on the one surface of the core layer and formed of a first resin composition, and the second resin layer provided on the other surface of the core layer and formed of a second resin composition, wherein at least one of a requirement that a thickness of the first resin layer is different from that of the second resin layer and a requirement that a constitution of the first resin composition is different from that of the second resin composition is satisfied.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of Ser. No. 12/085,782, filed Jul. 16,2009, which is a 371 National Phase entry of PCT/JP2006/323994, filedNov. 30, 2006 and claims the benefit of JP 2005-348546, filed Dec. 1,2005 and JP 2006-216432, filed Aug. 9, 2006, all of which are beingincorporated in their entirety herein by reference.

FIELD OF THE INVENTION

The present invention relates to a prepreg, a method for manufacturingthe prepreg, a substrate formed using the prepreg, and a semiconductordevice provided with the substrate.

BACKGROUND

A circuit substrate is formed using a prepreg obtained by impregnating asheet-shaped base member, such as a glass fiber base material, withthermosetting resin. For example, Japanese Patent Application Laid-openNo. 2004-216784 (hereinafter, simply referred to as “Patent Document 1”)discloses a method for manufacturing a prepreg by immersing a glassfiber base material having a thickness of about 50 to 200 μm into athermosetting resin varnish.

In a prepreg obtained by such a method, a resin composition is supportedby the glass fiber base material, and two resin layers formed of theresin composition are symmetrically provided on both surfaces (sides) ofthe glass fiber base material. More specifically, such a prepreg has astructure in which two resin layers formed of the same resin compositionand having the same thickness are provided on both the surfaces of theglass fiber base material.

Meanwhile, in recent years, electronic parts, electronic devices and thelike are becoming increasingly smaller and thinner, and thereforecircuit substrates and the like used for them are also required to besmaller and thinner. This leads to necessity for forming ahigher-density circuit wiring portion (circuit wiring pattern) in thecircuit substrates.

In order to form such a higher-density circuit wiring portion, amultilayer circuit substrate is used. In addition, various attempts havebeen made to reduce a thickness of each layer of the multilayer circuitsubstrate.

From a viewpoint of redaction of a thickness of a multilayer circuitsubstrate, generally, such a multilayer circuit substrate ismanufactured by preparing a plurality of prepregs each having a circuitwiring portion on one surface thereof, and laminating the prepregs sothat the circuit wiring portion provided on the one surface of theprepreg is embedded into an opposite surface of another prepreglaminated on the prepreg.

In this case, the one surface of the prepreg, on which the circuitwiring portion is to be formed, is required to have platingadhesiveness, and the other surface of the prepreg, into which a circuitwiring portion of the other prepreg is to be embedded, is required tohave embeddability (moldability) for filling gaps between wiresconstituting the circuit wiring portion.

However, as described above, the prepreg disclosed in Patent Document 1has two resin layers formed of the same resin composition on both thesurfaces of the base material. Therefore, it is difficult to select aresin composition which allows each resin layer to have both propertiesof the plating adhesiveness and the embeddability. Such a problembecomes particularly conspicuous in the case where an attempt is made toreduce the thickness of the prepreg.

Further, there is also a case that a circuit wiring portion is embeddedinto each of two resin layers of a prepreg.

However, in the case where two circuit wiring portions having adifferent size such as thickness are embedded into the prepreg disclosedin Patent Document 1, there is a case that an amount of the resincomposition constituting the resin layers becomes larger or smaller thana required amount of a resin composition to be filled in gaps betweenwires constituting each circuit wiring portion (hereinafter, also simplyreferred to as “gaps in a circuit wiring portion”).

As a result, there is a problem in that the resin composition issqueezed out of an obtained substrate from a side surface thereof, thecircuit wiring portion cannot be reliably embedded into the resin layeror the like.

As described above, it is difficult for the prepreg disclosed in PatentDocument 1 to satisfy the following two requirements: (A) the prepreghas both properties of the plating adhesiveness and the embeddability;and (B) an amount of a resin composition can be set appropriatelydepending on a circuit wiring portion to be embedded thereinto.

Further, it is also difficult to manufacture a prepreg using a thinglass fiber base material by a conventional method.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a prepregwhich can meet a demand for thickness reduction and which can have twosurfaces having different applications, functions, capabilities, orproperties.

Another object of the present invention is to provide a prepreg whichcan meet a demand for thickness reduction and which allows an amount ofa resin composition to be set appropriately depending on a circuitwiring portion to be embedded thereinto.

Yet another object of the present invention is to provide a method formanufacturing the prepreg according to the present invention, asubstrate using the prepreg according to the present invention, and asemiconductor device provided with the substrate according to thepresent invention.

In order to achieve the object described above, the present invention isdirected to a prepreg. The prepreg includes a core layer including asheet-shaped base member, the core layer having one surface and theother surface which is opposite to the one surface, a first resin layerprovided on the one surface of the core layer, the first resin layerformed of a first resin composition, and a second resin layer providedon the other surface of the core layer, the second resin layer formed ofa second resin composition.

In such a prepreg, it is required that at least one of a requirementthat a thickness of the first resin layer is different from that of thesecond resin layer and a requirement that a constitution of the firstresin composition is different from that of the second resin compositionis satisfied.

This makes it possible to provide a prepreg which can meet a demand forthickness reduction, and which can have two surfaces having differentapplications, functions, capabilities, or properties and/or which allowsan amount of a resin composition to be set appropriately depending on acircuit wiring portion to be embedded thereinto.

Further, in the prepreg of the present invention, it is preferred thatthe constitution of the first resin composition is different from thatof the second resin composition, and the prepreg is adapted to be usedin a state that a conductor layer is provided on the first resin layer.

Furthermore, in the prepreg of the present invention, it is alsopreferred that when the conductor layer is bonded to the first resinlayer, peel strength between the first resin layer and the conductorlayer is 0.5 kN/m or more.

Moreover, in the prepreg of the present invention, it is also preferredthat the thickness of the first resin layer is in the range of 3 to 15μm.

Moreover, in the prepreg of the present invention, it is also preferredthat the first resin composition contains thermosetting resin.

Moreover, in the prepreg of the present invention, it is also preferredthat the thermosetting resin contains cyanate resin.

Moreover, in the prepreg of the present invention, it is also preferredthat the cyanate resin contains novolak type cyanate resin.

Moreover, in the prepreg of the present invention, it is also preferredthat the first resin composition further contains a curing agent.

Moreover, in the prepreg of the present invention, it is also preferredthat the curing agent contains an imidazole based compound.

Moreover, in the prepreg of the present invention, it is also preferredthat the first resin composition further contains second resin whosekind is different from that of the thermosetting resin.

Moreover, in the prepreg of the present invention, it is also preferredthat the second resin contains phenoxy based resin.

Moreover, in the prepreg of the present invention, it is also preferredthat the thickness of the first resin layer is thinner than that of thesecond resin layer.

Further, in the prepreg of the present invention, it is also preferredthat the constitution of the first resin composition is identical withthat of the second resin composition, and the thickness of the firstresin layer is different from that of the second resin layer, and athickness of the sheet-shaped base member is 25 μm or less.

Furthermore, in the prepreg of the present invention, it is alsopreferred that a thickness of the prepreg is 35 μm or less.

Moreover, in the prepreg of the present invention, it is also preferredthat the resin composition contains thermosetting resin.

Moreover, in the prepreg of the present invention, it is also preferredthat the thermosetting resin contains cyanate resin.

Moreover, in the prepreg of the present invention, it is also preferredthat the resin composition further contains an inorganic filler.

The present invention is also directed to a method for manufacturing theabove prepreg. The method includes preparing the core layer, a firstsheet member having one surface on which the first resin composition isapplied in the form of a layer, and a second sheet member having onesurface on which the second resin composition is applied in the form ofa layer, laminating the core layer with the first sheet member and thesecond sheet member so that the first resin composition and the secondresin composition make contact with both surfaces of the core layer,respectively, whereby the core layer, the first sheet member and thesecond sheet member are joined together to obtain a laminate, andremoving bubbles from the laminate. This makes it possible tomanufacture the above prepreg easily and cheaply.

Further, in the method for manufacturing the prepreg of the presentinvention, it is also preferred that joining of the core layer, thefirst sheet member and the second sheet member is carried out underreduced pressure.

Furthermore, in the method for manufacturing the prepreg of the presentinvention, it is also preferred that removing of the bubbles from thelaminate is carried out by a heat treatment.

Moreover, in the method for manufacturing the prepreg of the presentinvention, it is also preferred that the heat treatment is carried outat a temperature of a melting point or higher, wherein the melting pointis a higher melting point than a melting point of the first resincomposition and a melting point of the second resin composition.

Moreover, in the method for manufacturing the prepreg of the presentinvention, it is also preferred that the first sheet member is formed ofa conductive material.

Moreover, in the method for manufacturing the prepreg of the presentinvention, it is also preferred that each of the first sheet member andthe second member is formed from a resin sheet, and the method furtherincludes after removing the bubbles from the laminate, removing theresin sheets from the laminate.

Moreover, in the method for manufacturing the prepreg of the presentinvention, it is also preferred that a surface of each of the resinsheets on which each resin composition is applied is subjected to arelease treatment.

The present invention is also directed to a substrate. The substrateincludes the above prepreg, and a circuit wiring portion embedded intothe second resin layer of the prepreg. This makes it possible to obtaina substrate having a thin thickness.

Further, in the substrate of the present invention, it is also preferredthat when a total thickness of the prepreg is defined by T0 μm and aheight of the circuit wiring portion is defined by t1 μm, a differenceof T0 and t1 is 35 μm or less.

Furthermore, in the substrate of the present invention, it is alsopreferred that thermal expansion coefficient of the prepreg at a planedirection thereof is 16 ppm or less.

The present invention is also directed to a substrate manufactured bylaminating a plurality of the above prepregs. This makes it possible toobtain a substrate having a thin thickness.

The present invention is also directed to a semiconductor device. Thesemiconductor device includes the above substrate, and a semiconductorelement mounted on the substrate. This makes it possible to obtain asemiconductor device having a thin thickness.

The present invention is also directed to a semiconductor device havingthe above substrate. This makes it possible to obtain a semiconductordevice having a thin thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing one example (first embodiment) of theprepreg according to the present invention.

FIG. 2 is a sectional view for explaining a thickness of a second resinlayer provided in the first embodiment of the prepreg.

FIG. 3 is a diagram showing one example of a process for manufacturingthe prepreg according to the present invention.

FIGS. 4( a) and 4(b) are sectional views each showing one example(second embodiment) of the prepreg according to the present invention.

FIG. 5 is a sectional view for explaining a relationship of thicknessesof two resin layers provided in the second embodiment of the prepregaccording to the present invention.

FIG. 6 is a sectional view showing one example of the substrateaccording to the present invention.

FIG. 7 is a sectional view showing one example of the semiconductordevice according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, a prepreg, a method for manufacturing the prepreg, asubstrate formed using the prepreg, and a semiconductor device providedwith the substrate according to the present invention will be described.

The prepreg according to the present invention includes a core layerincluding a sheet-shaped base member and having one surface and theother surface which is opposite to the one surface, a first resin layerprovided on the one surface of the core layer and formed of a firstresin composition, and a second resin layer provided on the othersurface of the core layer and formed of a second resin composition.

Further, the prepreg is adapted to be used in a state that a conductorlayer is provided (formed) on the first resin layer. Furthermore, theprepreg satisfies at least one of a requirement that a thickness of thefirst resin layer is different from that of the second resin layer and arequirement that a constitution of the first resin composition isdifferent from that of the second resin composition.

The method for manufacturing the prepreg according to the presentinvention includes preparing the core layer, a first sheet member havingone surface on which the first resin composition is applied in the formof a layer, and a second sheet member having one surface on which thesecond resin composition is applied in the form of a layer, laminatingthe core layer with the first sheet member and the second sheet memberso that the first resin composition and the second resin compositionmake contact with both surfaces of the core layer, respectively, wherebythe core layer, the first sheet member and the second sheet member arejoined together to obtain a laminate, and removing bubbles from thelaminate.

Further, the substrate according to the present invention includes theprepreg according to the present invention and a circuit wiring portionembedded into the second resin layer of the prepreg.

Furthermore, the semiconductor device according to the present inventionincludes the substrate according to the present invention and asemiconductor element mounted on the substrate.

First Embodiment

First, a preferred embodiment (first embodiment) of the prepregaccording to the present invention will be described based on theaccompanying drawings.

FIG. 1 is a sectional view showing one example (first embodiment) of theprepreg according to the present invention. In this regard, it is to benoted that, in the following description, the upper side and the lowerside in FIG. 1 will be referred to as “upper side” and “lower side”,respectively (the same goes for other drawings).

A prepreg (that is, a resin film for forming a multilayer wiringsubstrate) 10 includes a core layer 11 having a sheet-shaped base member(that is, a fiber base member) 1, a first resin layer 2 provided on onesurface of the core layer 11, and a second resin layer 3 provided on theother surface of the core layer 11.

The first resin layer 2 of the prepreg 10 is formed of a first resincomposition, and the second resin layer 3 of the prepreg 10 is formed ofa second resin composition. In this embodiment, a constitution(composition) of the first resin composition is different from that ofthe second resin composition.

This makes it possible to design a formulation of a resin compositionfor each resin layer so that each resin layer can have desiredproperties, thereby reducing a total thickness of the prepreg 10 whileallowing two resin layers thereof to have their respective desiredproperties.

The prepreg 10 shown in FIG. 1 is adapted to be used in a state that aconductor layer (not shown in the drawing) is provided on the firstresin layer 2 (that is, an upper surface of the prepreg 10 in FIG. 1).Therefore, the first resin layer 2 is designed to have good adhesivenessto the conductor layer.

Further, since the second resin layer 3 is required to have propertiesdifferent from those of the first resin layer 2, the second resin layer3 is designed to satisfy such a requirement.

Hereinbelow, the core layer 11, the first resin layer 2, and the secondresin layer 3 will be described in more detail in the named order.

(Core Layer)

The core layer 11 is mainly constituted from the sheet-shaped basemember 1. The core layer 11 has a function of enhancing strength of theprepreg 10.

The core layer 11 may be constituted from the sheet-shaped base member 1alone, or may be constituted from the sheet-shaped base member 1 inwhich a part of the first resin layer 2 and a part of the second resinlayer 3 are impregnated on the both surfaces thereof, respectively.

Examples of such a sheet-shaped base member 1 include: a fiber basemember such as a glass fiber base member (e.g., a glass woven cloth, aglass non-woven cloth), an organic fiber base member such as a syntheticfiber base member formed from a woven or non-woven cloth mainly made ofpolyamide-based resin fibers (e.g., polyamide resin fibers, aromaticpolyamide resin fibers, wholly aromatic polyamide resin fibers),polyester-based resin fibers (e.g., polyester resin fibers, aromaticpolyester resin fibers, wholly aromatic polyester resin fibers),polyimide resin fibers or fluorocarbon resin fibers, or a paper basemember mainly formed from kraft paper, cotton linter paper or blendedpaper of linter and kraft pulp; a resin film such as a polyester film ora polyimide film; and the like.

Among these sheet-shaped base members, the glass fiber base member ispreferably used. By using such a sheet-shaped base member, it ispossible to enhance strength of the prepreg 10. In addition, it is alsopossible to reduce a thermal expansion coefficient of the prepreg 10.

Examples of a glass material for forming the glass fiber base memberinclude E glass, C glass, A glass, S glass, D glass, NE glass, T glass,H glass, and the like. Among these glass materials, the S glass and theT glass are preferably used. By using such a glass material, it ispossible to reduce a thermal expansion coefficient of the glass fiberbase member, thereby reducing the thermal expansion coefficient of theprepreg 10.

A thickness of the sheet-shaped base member (fiber base member) 1 is notparticularly limited to a specific value, but is preferably 30 μm orless, more preferably 25 μm or less, and most preferably in the range of10 to 20 μm, thereby enabling a thickness of the prepreg 10 to bereduced.

By setting the thickness of the sheet-shaped base member 1 to a valuewithin the above range, it is possible to reduce a thickness of anobtained substrate (which will be described later) while maintainingstrength thereof. In addition, it is also possible to obtain a prepreg10 having excellent workability for establishing interlayer connectionand therefore to allow an obtained substrate to have excellentreliability of interlayer connection.

Here, it is to be noted that the phrase “workability for establishinginterlayer connection” used herein means that upper and lower circuitwiring portions (that is, patterned conductor layers) can be easilyconnected to each other when a multilayered circuit substrate(hereinafter, also simply referred to as a “multilayer substrate”) ismanufactured.

Further, the phrase “reliability of interlayer connection (connectionreliability)” used herein means that in an obtained multilayersubstrate, upper and lower circuit wiring portions are reliablyconnected to each other and a short circuit does not occur between wallsof through holes or via holes formed.

(First Resin Layer)

As shown in FIG. 1, the first resin layer 2 is provided on the onesurface (upper surface in FIG. 1) of the core layer 11. As describedabove, the first resin layer 2 is formed of the first resin composition,and the first resin composition is designed to have good adhesiveness toa conductor layer to be provided on the first resin layer 2 (not shownin the drawing).

Such a first resin composition having good adhesiveness to the conductorlayer contains curable resin, and further may contain at least one of acuring aid (e.g., a curing agent, a curing accelerator), an inorganicfiller and the like, if necessary.

Examples of a method for improving adhesiveness between the first resincomposition and the conductor layer include use of curable resin havinggood adhesiveness to the conductor layer, use of a curing aid (e.g., acuring agent, a curing accelerator) which can improve adhesivenessbetween the first resin composition and the conductor layer, use of anacid-soluble inorganic filler, use of an inorganic filler in combinationwith an organic filler, and the like.

As the curable resin having good adhesiveness to the conductor layer,thermosetting resin such as urea resin, melamine resin, bismaleimideresin, polyurethane resin, benzoxazine ring-containing resin, cyanateester resin, bisphenol S type epoxy resin, bisphenol F type epoxy resin,or copolymeric epoxy resin of bisphenol S and bisphenol F is preferablyused. Among these curable resins, cyanate resin (including a prepolymerof the cyanate resin) is more preferably used.

By using such thermosetting resin (especially, cyanate resin), it ispossible to reduce the thermal expansion coefficient of the prepreg 10(hereinafter, also referred to as “it is possible to allow the prepreg10 to have lower thermal expansivity”). In addition, it is also possibleto improve electric properties of the prepreg 10 such as low-dielectricconstant, low dielectric loss tangent and the like.

The cyanate resin can be obtained by, for example, a reaction ofcyanogen halide and phenol to thereby produce a prepolymer. Ifnecessary, a heat treatment may be carried out during the reaction.

Specifically, examples of such cyanate resin include novolak typecyanate resin, bisphenol type cyanate resin such as bisphenol A typecyanate resin, bisphenol E type cyanate resin or tetramethylbisphenol Ftype cyanate resin, and the like. Among these cyanate resins, thenovolak type cyanate resin is preferably used.

By using the novolak type cyanate resin, it is possible for a curedfirst resin composition constituting a cured first resin layer 2 in anobtained substrate to have an increased crosslink density, therebyimproving heat resistance and flame retardancy of the cured first resinlayer 2 (obtained substrate).

In this regard, it can be supposed that the improved heat resistance isachieved due to existence of triazine rings formed in the cured firstresin composition by the curing reaction of the novolak type cyanateresin.

Also, it can be supposed that the improved flame retardancy is achieveddue to formation of carbonized portions in the cured first resin layer2. This is because the novolak type cyanate resin has a high content ofbenzene rings due to its structure, and the benzene rings contained inthe novolak type cyanate resin are easily carbonized (graphitized).

In addition, by using the novolak type cyanate resin, it is alsopossible for the prepreg 10 to have excellent rigidity even in the casewhere the prepreg 10 has a reduced thickness (e.g., 35 μm or less). Thecyanate resin or a cured product thereof offers excellent rigidityparticularly upon heating, and therefore an obtained substrate offersespecially excellent reliability when a semiconductor element is mountedthereon.

As the novolak type cyanate resin, one represented by, for example, thefollowing formula (I) can be used.

wherein n is any integer.

An average number of repeating units n of the novolak type cyanate resinrepresented by the above formula (I) is not particularly limited to aspecific value, but is preferably in the range of 1 to 10, and morepreferably in the range of 2 to 7.

If the average number of repeating units n is less than the above lowerlimit value, the novolak type cyanate resin tends to be crystallized,thereby relatively reducing solubility of the novolak type cyanate resinin general purpose-solvents.

As a result, there is a case that it is difficult to handle a varnishcontaining the first resin composition (that is, a varnish for forming afirst resin layer) depending on an amount of the novolak type cyanateresin contained in the varnish, and the like.

In addition, in this case, since the prepregs 10 are likely to becometacky, there is also a case that when one prepreg 10 makes contact withanother prepreg 10, the prepregs 10 adhere to each other, or the firstresin composition of the one prepreg 10 is transferred to the anotherprepreg 10.

On the other hand, if the average number of repeating units n exceedsthe above upper limit value, a melt viscosity of the first resincomposition becomes too high, and therefore there is a case thatmanufacturing efficiency (moldability) of the prepreg 10 is reduced.

In this regard, it is to be noted that a weight average molecular weightof the cyanate resin or the like can be measured using, for example, aGPC (gel permeation chromatography).

In this regard, it is to be noted that the cyanate resin may be used asa prepolymer obtained by polymerizing two or more molecules of thecyanate resin. More specifically, the cyanate resin may be used singlyor in combination with the prepolymer. Alternatively, two or morecyanate resins having different weight average molecular weights may beused in combination.

Such a prepolymer can be usually obtained by, for example, polymerizingthree molecules of the cyanate resin (trimerizing molecules of thecyanate resin) by a heating reaction, and is preferably used to controlmoldability or flowability of the resin composition.

The prepolymer is not particularly limited to a specific type, but it ispreferred that a prepolymer containing a trimer at an amount of 20 to 50wt % can be used. In this regard, it is to be noted that the amount ofthe trimer (trimeric structure of the cyanate resin) contained in theprepolymer can be determined using, for example, an infraredspectroscopic analyzer.

In the case where the curable resin is used in combination with a curingagent or a curing accelerator which improves adhesiveness between thefirst resin composition and the conductor layer (which will be describerlater), thermosetting resin other than the above-mentioned curable resinhaving good adhesiveness to the conductor layer may be used.

Examples of such a thermosetting resin include: phenolic resin such asnovolak type phenolic resin (e.g., phenol novolak resin, cresol novolakresin, bisphenol A novolak resin), or resol type phenolic resin (e.g.,non-modified resol phenolic resin, oil-modified resol phenolic resinmodified with oil such as wood oil, linseed oil or walnut oil); epoxyresin such as bisphenol type epoxy resin (e.g., bisphenol A epoxy resin,bisphenol F epoxy resin), novolak type epoxy resin (e.g., novolak epoxyresin, cresol novolak epoxy resin), or biphenyl type epoxy resin;unsaturated polyester resin; diallyl phthalate resin; silicone resin;and the like.

In this regard, it is to be noted that as the curable resin, UV curableresin, anaerobic curable resin or the like may be used instead of thethermosetting resin or in addition to the thermosetting resin.

An amount of the curable resin contained in the first resin compositionis not particularly limited to a specific value, but is preferably inthe range of 5 to 50 wt %, and more preferably in the range of 10 to 40wt % with respect to a total weight of the first resin composition.

If the amount of the curable resin contained in the first resincomposition is less than the above lower limit value, there is a casethat it is difficult to manufacture the prepreg 10 depending on a meltviscosity of the first resin composition and the like.

On the other hand, if the amount of the curable resin contained in thefirst resin composition exceeds the above upper limit value, there is acase that strength of the prepreg 10 is reduced or lowered depending ona kind of the curable resin used, a weight average molecular weight ofthe curable resin and the like.

Examples of a curing aid (e.g., a curing agent, a curing accelerator)which improves adhesiveness between the first resin composition and theconductor layer include: tertiary amine such as triethylamine,tributylamine, or diazabicyclo[2,2,2]octane; an imidazole compound suchas 2-ethyl-4-ethylimidazole, 2-phenyl-4-methylimidazole,2-phenyl-4-methyl-5-hydroxymethylimidazole,2-phenyl-4,5-dihydroxymethylimidazole,2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine,2,4-diamino-6-(2′-undecylimidazolyl)-ethyl-s-triazine,2,4-diamino-6-[2′-ethyl-4-methylimidazolyl-(1′)]-ethyl-s-triazine, or1-benzyl-2-phenylimidazole; and the like.

Among these curing aids, an imidazole compound having two or morefunctional groups each selected from an aliphatic hydrocarbon group, anaromatic hydrocarbon group, a hydroxyalkyl group, and a cyanoalkyl groupis preferably used, and 2-phenyl-4,5-dihydroxymethylimidazole is morepreferably used.

By using such an imidazole compound, it is possible to improve heatresistance of the first resin composition as well as to give low thermalexpansivity (that is, a property such that an expansion coefficientcaused by heat is low) and a low water-absorbing property to the firstresin layer 2 formed of the first resin composition.

Further, in the case where the curable resin having good adhesiveness tothe conductor layer is used as the curable resin, a material other thanthe above-mentioned curing aid which improves adhesiveness between thefirst resin composition and the conductor layer may be used incombination with the curable resin.

Examples of such a material include: organometallic salt such as zincnaphthenate, cobalt naphthenate, tin octylate, cobalt octylate, cobalt(II) bisacetylacetonate, or cobalt (III) triacetylacetonate; a phenolcompound such as phenol, bisphenol A, or nonylphenol; organic acid suchas acetic acid, benzoic acid, salicylic acid, or paratoluenesulfonicacid; and the like.

In the case where the curing aid is used, an amount of the curing aidcontained in the first resin composition is not particularly limited toa specific value, but is preferably in the range of 0.01 to 3 wt %, andmore preferably in the range of 0.1 to 1 wt % with respect to a totalweight of the first resin composition.

If the amount of the curing aid contained in the first resin compositionis less than the above lower limit value, there is a case that an effectof accelerating curing of the curable resin (first resin composition)cannot be sufficiently obtained depending on a kind of the curing aidused, and the like.

On the other hand, if the amount of the curing aid contained in thefirst resin composition exceeds the above upper limit value, there is acase that stability of the prepreg 10 during storage (storage stability)is reduced.

In this regard, it is to be noted that from the viewpoint of allowingthe first resin layer 2 to have further improved adhesiveness to theconductor layer, the curable resin having good adhesiveness to theconductor layer is preferably used together with the curing aid whichimproves adhesiveness between the first resin composition and theconductor layer.

Further, the first resin composition preferably contains an inorganicfiller. This makes it possible to obtain a prepreg 10 having highstrength while having a reduced thickness (e.g., 35 μm or less). Inaddition, it is also possible to allow the prepreg 10 to have improvedlower thermal expansivity.

Examples of the inorganic filler include talc, alumina, glass, silica,mica, aluminum hydroxide, magnesium hydroxide, and the like. Among theseinorganic fillers, the silica is preferably used. From the viewpoint ofexcellent low thermal expansivity, molten silica (especially, sphericalmolten silica) is preferably used.

The inorganic filler (that is, the particles thereof) may have a crushedshape or a spherical shape, but a shape of the inorganic filler isappropriately selected according to its purpose of use. For example, inorder to impregnate the sheet-shaped base member 1 with the first resincomposition reliably, it is preferred that a melt viscosity of the firstresin composition is reduced. In this case, spherical silica ispreferably used as the inorganic filler.

An average particle size of the inorganic filler is not particularlylimited to a specific value, but is preferably in the range of 0.01 to5.0 μm, and more preferably in the range of 0.2 to 2.0 μm.

If the average particle size of the inorganic filler is less than theabove lower limit value, there is a case that the viscosity of the firstresin composition in a molten state (melt viscosity) becomes highdepending on an amount of the inorganic filler contained in the firstresin composition, and the like, thereby affecting workability duringmanufacture of the prepreg 10.

On the other hand, if the average particle size of the inorganic fillerexceeds the above upper limit value, there is a case that a phenomenonsuch as sedimentation of the inorganic filler in a varnish for forming afirst resin layer occurs.

In contrast, by setting the average particle size of the inorganicfiller to a value within the above range, it is possible to exhibit theeffects obtained by using the inorganic filler in a fine balance.

In this regard, it is to be noted that the average particle size of theinorganic filler can be measured by, for example, a particle sizedistribution analyzer (“LA-500” produced by HORIBA).

As the inorganic filler, spherical silica (especially, spherical moltensilica) is preferably used. An average particle size of the sphericalmolten silica is preferably 5.0 μm or less, more preferably in the rangeof 0.01 to 2.0 μm, and most preferably in the range of 0.1 to 0.5 μm.

By using such spherical silica as the inorganic filler, it is possibleto improve a filling factor (packing density) of the inorganic fillerwithin the first resin layer 2. In addition, it is also possible toallow the first resin layer 2 to have an upper surface finely roughened,namely, it is possible to allow the upper surface of the first resinlayer 2 to have a relatively small surface roughness.

This makes it possible to form the conductor layer on the first resinlayer 2 in a state that these layers make close contact with each other,and therefore to easily form a circuit wiring portion (circuit wiringpattern) having a high wiring density (high-density circuit). Inaddition, it is also possible to form a circuit wiring portion suitablefor transmitting signals high speed.

The inorganic filler to be used for the first resin composition is notparticularly limited to a specific type, but it is preferred that it hasan average particle size smaller than that of an inorganic filler to beused for the second resin composition (which will be described later).By using such an inorganic filler, it becomes easy to allow the firstresin layer 2 to have an upper surface finely roughened.

Further, in order to improve adhesiveness between the first resin layer2 and the conductor layer, an acid-soluble inorganic filler may also beused as the inorganic filler. By using the acid-soluble inorganicfiller, it is possible to improve adhesiveness (plating adhesiveness) ofthe first resin layer 2 to the conductor layer in the case where theconductor layer is formed on the first resin layer 2 by a platingmethod.

Examples of the acid-soluble inorganic filler include calcium carbonate,metal oxide such as zinc oxide or iron oxide, and the like.

Furthermore, in order to improve adhesiveness between the first resinlayer 2 and the conductor layer, the inorganic filler may be used incombination with an organic filler.

Examples of such an organic filler include a resin-based filler such asliquid crystal polymer or polyimide, and the like.

In the case where the inorganic filler is used, an amount of theinorganic filler contained in the first resin composition is notparticularly limited to a specific value, but is preferably in the rangeof 20 to 70 wt %, and more preferably in the range of 30 to 60 wt % withrespect to a total weight of the first resin composition.

If the amount of the inorganic filler contained in the first resincomposition is less than the above lower limit value, there is a casethat an effect obtained by using the inorganic filler, which gives lowthermal expansivity and a low water-absorbing property to the firstresin layer 2, is reduced depending on a kind of the inorganic fillerused, and the like.

On the other hand, if the amount of the inorganic filler contained inthe first resin composition exceeds the above upper limit value, thereis a case that flowability of the first resin composition is lowered sothat moldability of the first resin layer 2 (prepreg 10) is lowered.

In contrast, by setting the amount of the inorganic filler contained inthe first resin composition to a value within the above range, it ispossible to exhibit the effects obtained by using the inorganic fillerin a fine balance.

In the case where the cyanate resin (especially, novolak type cyanateresin) is used as the curable resin, epoxy resin (which containssubstantially no halogen atom) is preferably used in combination withthe cyanate resin. Examples of the epoxy resin include phenol novolaktype epoxy resin, bisphenol type epoxy resin, naphthalene type epoxyresin, arylalkylene type epoxy resin, and the like.

Among these epoxy resins, the arylalkylene type epoxy resin ispreferably used. By using such epoxy resin, it is possible for a curedfirst resin layer 2 (obtained substrate) to have improved solder heatresistance after moisture absorption and flame retardancy.

The arylalkylene type epoxy resin is epoxy resin having one or morearylalkylene groups in one repeating unit. Examples of such arylalkylenetype epoxy resin include xylylene type epoxy resin, biphenyldimethylenetype epoxy resin, and the like. Among these arylalkylene type epoxyresins, the biphenyldimethylene type epoxy resin is preferably used.

The biphenyldimethylene type epoxy resin can be represented by, forexample, the following formula (II).

wherein n is any integer.

An average number of repeating units n of the biphenyldimethylene typeepoxy resin represented by the above formula (II) is not particularlylimited to a specific value, but is preferably in the range of 1 to 10,and more preferably in the range of 2 to 5.

If the average number of repeating units n is less than the above lowerlimit value, the biphenyldimethylene type epoxy resin tends to becrystallized, thereby reducing solubility of the biphenyldimethylenetype epoxy resin in general purpose-solvents. As a result, there is acase that it becomes difficult to handle a varnish for forming a firstresin layer.

On the other hand, if the average number of repeating units n exceedsthe above upper limit value, there is a case that flowability of thefirst resin composition in a molten state is reduced, thereby causingdefective molding of the prepreg 10, and the like.

In the case where a combination of the epoxy resin and the cyanate resinis used as the curable resin, an amount of the epoxy resin contained inthe first resin composition is not particularly limited to a specificvalue, but is preferably in the range of 1 to 55 wt %, and morepreferably in the range of 2 to 40 wt % with respect to a total weightof the first resin composition.

If the amount of the epoxy resin contained in the first resincomposition is less than the above lower limit value, there is a casethat reactivity of the cyanate resin is lowered or moisture resistanceof the first resin layer 2 is lowered.

On the other hand, if the amount of the epoxy resin contained in thefirst resin composition exceeds the above upper limit value, there is acase that heat resistance of the first resin layer 2 is lowereddepending on a kind of the epoxy resin used, and the like.

A weight average molecular weight of the epoxy resin is not particularlylimited to a specific value, but is preferably in the range of 300 to20,000, and more preferably in the range of 500 to 5,000.

If the weight average molecular weight of the epoxy resin is less thanthe above lower limit value, there is a case that the prepreg 10 becomestacky depending on ambient temperature, and the like.

On the other hand, if the weight average molecular weight of the epoxyresin exceeds the above upper limit value, there is a case that itbecomes difficult to impregnate the sheet-shaped base member 1 (corelayer 11) with the first resin composition in the manufacturing processof the prepreg 10, and therefore a prepreg 10 having uniform thicknessand uniform quality cannot be obtained.

In this regard, it is to be noted that the weight average molecularweight of the epoxy resin can be measured using, for example, a GPC (gelpermeation chromatography).

The first resin composition may further contain a component (which maybe resin or the like) which improves adhesiveness between the firstresin layer 2 and the conductor layer. Examples of such a componentinclude phenoxy resin, polyvinyl alcohol-based resin, a coupling agentwhich improves adhesiveness between the first resin layer 2 and a metalconstituting the conductor layer, and the like.

Examples of the phenoxy resin include phenoxy resin having bisphenolskeletons, phenoxy resin having naphthalene skeletons, phenoxy resinhaving biphenyl skeletons, and the like. Alternatively, phenoxy resinhaving two or more kinds of these skeletons may also be used.

Among these phenoxy resins, phenoxy resin having biphenyl skeletons andbisphenol S skeletons is preferably used. Such phenoxy resin has a highglass transition temperature due to rigidity resulting from the biphenylskeletons and has improved adhesiveness to a metal constituting theconductor layer resulting from the bisphenol S skeletons.

Therefore, by using such phenoxy resin, it is possible to improve heatresistance of the first resin layer 2 and adhesiveness between the firstresin layer 2 and a plated metal when a multilayer substrate (multilayerprinted wiring board) is manufactured.

Also, phenoxy resin having bisphenol A skeletons and bisphenol Fskeletons is preferably used. By using such phenoxy resin, it ispossible to further improve adhesiveness between the first resin layer 2and a circuit wiring portion (inner layer circuit) when a multilayerprinted wiring board is manufactured.

More preferably, the phenoxy resin having biphenyl skeletons andbisphenol S skeletons and the phenoxy resin having bisphenol A skeletonsand bisphenol F skeletons are used in combination. By doing so, it ispossible to allow the prepreg 10 to have properties resulting from thesephenoxy resins in a fine balance.

In the case where the phenoxy resin (1) having bisphenol A skeletons andbisphenol F skeletons and the phenoxy resin (2) having biphenylskeletons and bisphenol S skeletons are used in combination, the ratio(weight ratio) between (1) and (2) is not particularly limited to aspecific value, but can be set to a range of, for example, 2:8 to 9:1.

A molecular weight of the phenoxy resin is not particularly limited to aspecific value, but a weight average molecular weight of the phenoxyresin is preferably in the range of 5,000 to 70,000, and more preferablyin the range of 10,000 to 60,000.

If the weight average molecular weight of the phenoxy resin is less thanthe above lower limit value, there is a case that it is impossible tosufficiently give an effect of improving film formability (that is, easeof film formation) to the first resin composition depending on a kind ofthe phenoxy resin used, and the like.

On the other hand, if the weight average molecular weight of the phenoxyresin exceeds the above upper limit value, there is a case thatsolubility of the phenoxy resin is reduced depending on a kind of asolvent used, and the like.

In contrast, by setting the weight average molecular weight of thephenoxy resin to a value within the above range, it is possible toexhibit the effects obtained by using the phenoxy resin in a finebalance.

In the case where the phenoxy resin is used, an amount of the phenoxyresin contained in the first resin composition is not particularlylimited to a specific value, but is preferably in the range of 1 to 40wt %, and more preferably in the range of 5 to 30 wt % with respect to atotal weight of the first resin composition.

If the amount of the phenoxy resin contained in the first resincomposition is less than the above lower limit value, there is a casethat it is impossible to sufficiently give an effect of improving filmformability (that is, ease of film formation) to the first resincomposition depending on a kind of the phenoxy resin used, and the like.

On the other hand, if the amount of the phenoxy resin contained in thefirst resin composition exceeds the above upper limit value, an amountof the curable resin contained in the first resin composition becomesrelatively small.

Therefore, in the case where the cyanate resin is used as the curableresin, there is a case that an effect of giving low thermal expansivityto the first resin layer 2 is reduced depending on a kind of the cyanateresin used, a kind of the phenoxy resin used, and the like.

In contrast, by setting the amount of the phenoxy resin contained in thefirst resin composition to a value within the above range, it ispossible to exhibit the effects obtained by using the phenoxy resin in afine balance.

Further, it is preferred that a coupling agent is added to (mixed with)the first resin composition. The coupling agent has a function ofimproving wettability of an interface between the curable resin and theinorganic filler.

Therefore, by adding such a coupling agent to the first resincomposition, it is possible to uniformly fix the curable resin and theinorganic filler to the sheet-shaped base member 1. This makes itpossible to improve heat resistance of the first resin layer 2,especially solder heat resistance after moisture absorption of the curedfirst resin layer 2.

Examples of the coupling agent include an epoxy silane coupling agent, atitanate-based coupling agent, an amino silane coupling agent, asilicone oil type coupling agent, and the like, and one or more of thesecoupling agents are preferably used.

By using such a coupling agent, it is possible to particularly improvethe wettability of the interface between the curable resin and theinorganic filler, thereby further improving the heat resistance of thefirst resin layer 2.

In the case where the coupling agent is used, an amount of the couplingagent contained in the first resin composition is not particularlylimited to a specific vale, but is preferably in the range of 0.05 to 3parts by weight, and more preferably in the range of 0.1 to 2 parts byweight with respect to 100 parts by weight of the inorganic filler.

If the amount of the coupling agent contained in the first resincomposition is less than the above lower limit value, there is a casethat it is impossible to sufficiently cover a surface of the inorganicfiller with the coupling agent depending on a kind of the coupling agentused, a kind, shape or size of the inorganic filler used, and the like,thereby reducing an effect of improving the heat resistance of the firstresin layer 2.

On the other hand, if the amount of the coupling agent contained in thefirst resin composition exceeds the above upper limit value, there is acase that the coupling agent affects a curing reaction of the curableresin depending on a kind of the curable resin used, and the like,thereby reducing bending strength of a cured first resin layer 2(obtained substrate).

In contrast, by setting the amount of the coupling agent contained inthe first resin composition to a value within the above range, it ispossible to exhibit the effects obtained by using the coupling agent ina fine balance.

If necessary, the first resin composition may further contain one ormore additives such as an antifoaming agent, a leveling agent, a pigmentand an antioxidant, in addition to the above-described component.

A thickness of the first resin layer 2 formed of the first resincomposition is not particularly limited to a specific value, but ispreferably in the range of 3 to 15 μm, and more preferably in the rangeof 5 to 10 μm. By setting the thickness of the first resin layer 2 to avalue within the above range, it is possible to reduce a total thicknessof the prepreg 10.

A surface roughness of an upper surface of the first resin layer 2,which has been subjected to a surface-roughening treatment, is notparticularly limited to a specific value, but is preferably 2 μm orless, and more preferably 0.5 μm or less.

By setting the surface roughness of the upper surface of the first resinlayer 2 to a value within the above range, it is possible to allow theupper surface of the first resin layer 2 to have especially excellentadhesiveness to a resist used for forming a circuit wiring portion.Therefore, it is possible to form a fine circuit wiring portion on thefirst resin layer 2.

Examples of the conductor layer to be formed on the first resin layer 2include a metal foil such as a copper foil or an aluminum foil, a copperplating film, and the like. Among these conductor layers, the copperplating film is preferably used. By using such a conductor layer, it ispossible to easily form a fine circuit wiring portion on the first resinlayer 2.

Peel strength between the first resin layer 2 and the conductor layer(circuit wiring portion) is preferably 0.5 kN/m or more, and morepreferably 0.6 kN/m or more. By setting the peel strength between thefirst resin layer 2 and the conductor layer to a value within the aboverange, it is possible to further improve connection reliability of anobtained substrate (multilayer substrate).

(Second Resin Layer)

As shown in FIG. 1, the second resin layer 3 is provided on the othersurface (lower surface in FIG. 1) of the core layer 11. According to thepresent embodiment, as described above, the second resin layer 3 isformed of the second resin composition whose constitution is differentfrom that of the first resin composition.

As a result, the second resin layer 3 is designed to have propertiesdifferent from those of the first resin layer 2. Examples of theseproperties include circuit wiring portion embeddability and the like.

In this regard, it is to be noted that the phrase “a constitution of thesecond resin composition is different from that of the first resincomposition” means that at least one of a kind of the resin or fillerconstituting the second resin composition, an amount of the resin orfiller contained in the second resin composition, a molecular weight ofthe resin contained in the second resin composition, and the like isdifferent from that of the first resin composition.

The second resin composition contains curable resin, and in addition tothe curable resin it may further contain at least one of a curing agent,a curing accelerator, a filler and the like, if necessary.

Examples of the curable resin include: thermosetting resin such asphenolic resin such as novolak type phenolic resin (e.g., phenol novolakresin, cresol novolak resin, bisphenol A novolak resins), or resol typephenolic resins (e.g., non-modified resol phenolic resin, oil-modifiedresol phenolic resin modified with oil such as wood oil, linseed oil orwalnut oil); epoxy resins such as bisphenol type epoxy resin (e.g.,bisphenol A epoxy resin, bisphenol F epoxy resin), novolak type epoxyresin (e.g., novolak epoxy resin, cresol novolak epoxy resin), orbiphenyl-type epoxy resin; urea resin; triazine ring-containing resinsuch as melamine resin; unsaturated polyester resin; bismaleimide resin;polyurethane resin; diallylphthalate resin; silicone resin; benzoxazinering-containing resin; cyanate resin; and the like.

Among these curable resins, cyanate resin (which may be prepolymerthererof) is more preferably used. By using such curable resin(especially, cyanate resin), it is possible to reduce a thermalexpansion coefficient of the prepreg 10. In addition, it is alsopossible to allow the prepreg 10 to have excellent electric propertiessuch as low-dielectric constant and low dielectric loss tangent, and thelike.

The cyanate resin can be obtained by, for example, a reaction ofcyanogen halide and phenol to thereby produce a prepolymer. Ifnecessary, a heat treatment may be carried out during the reaction.

Specifically, examples of such cyanate resin include novolak typecyanate resin, bisphenol type cyanate resin such as bisphenol A typecyanate resin, bisphenol E type cyanate resin or tetramethylbisphenol Ftype cyanate resin, and the like. Among these cyanate resins, thenovolak type cyanate resin is preferably used.

By using the novolak type cyanate resin, it is possible for a curedsecond resin composition constituting a cured second resin layer 3 in anobtained substrate to have an increased crosslink density, therebyimproving heat resistance and flame retardancy of the cured second resinlayer 3 (obtained substrate).

In this regard, it can be supposed that the improved heat resistance isachieved due to existence of triazine rings formed in the cured secondresin composition by the curing reaction of the novolak type cyanateresin.

Also, it can be supposed that the improved flame retardancy is achieveddue to formation of carbonized portions in the cured second resin layer3. This is because the novolak type cyanate resin has a high content ofbenzene rings due to its structure, and the benzene rings contained inthe novolak type cyanate resin are easily carbonized (graphitized).

In addition, by using the novolak type cyanate resin, it is alsopossible for the prepreg 10 to have excellent rigidity even in the casewhere the prepreg 10 has a reduced thickness (e.g., 35 μm or less). Thecyanate resin or a cured product thereof offers excellent rigidityparticularly upon heating, and therefore an obtained substrate offersespecially excellent reliability when a semiconductor element is mountedthereon.

As the novolak type cyanate resin, one represented by, for example, thefollowing formula (I) can be used.

wherein n is any integer.

An average number of repeating units n of the novolak type cyanate resinrepresented by the above formula (I) is not particularly limited to aspecific value, but is preferably in the range of 1 to 10, and morepreferably in the range of 2 to 7.

If the average number of repeating units n is less than the above lowerlimit value, the novolak type cyanate resin tends to be crystallized,thereby reducing solubility of the novolak type cyanate resin in generalpurpose-solvents.

As a result, there is a case that it is difficult to handle a varnishcontaining the second resin composition (that is, a varnish for forminga second resin layer) depending on an amount of the novolak type cyanateresin contained in the varnish, and the like.

On the other hand, if the average number of repeating units n exceedsthe above upper limit value, a melt viscosity of the second resincomposition becomes too high, and therefore there is a case thatmanufacturing efficiency (moldability) of the prepreg 10 is reduced.

A weight average molecular weight of the cyanate resin is notparticularly limited to a specific value, but is preferably in the rangeof 500 to 4,500, and more preferably in the range of 600 to 3,000.

If the weight average molecular weight of the cyanate resin is less thanthe above lower limit value, since the prepregs 10 are likely to becometacky, there is a case that when one prepreg 10 makes contact withanother prepreg 10, the prepregs 10 adhere to each other, or the secondresin composition of the one prepregs 10 is transferred to the anotherprepreg 10.

On the other hand, if the weight average molecular weight of the cyanateresin exceeds the above upper limit value, there is a case that areaction rate of the cyanate resin becomes too high, thereby causingdefective molding of a substrate (especially, circuit substrate) orlowering interlayer peel strength of the substrate.

In this regard, it is to be noted that the weight average molecularweight of the cyanate resin can be measured using, for example, a GPC(gel permeation chromatography).

Further, the cyanate resin may be used in combination with anothercyanate resin having a different weight average molecular weight. Bydoing so, there is a case that a tackiness of the prepreg 10 can beimproved. In this regard, it is to be noted that as the curable resin,UV curable resin, anaerobic curable resin or the like may be used, inaddition to the thermosetting resin.

An amount of the curable resin contained in the second resin compositionis not particularly limited to a specific value, but is preferably inthe range of 5 to 50 wt %, and more preferably in the range of 20 to 40wt % with respect to a total weight of the second resin composition.

If the amount of the curable resin contained in the second resincomposition is less than the above lower limit value, there is a casethat it becomes difficult to form the prepreg 10 depending on a meltviscosity of the second resin composition and the like.

On the other hand, if the amount of the curable resin contained in thesecond resin composition exceeds the above upper limit value, there is acase that mechanical strength of the prepreg 10 is lowered depending ona kind of the curable resin used, a weight average molecular weight ofthe curable resin and the like.

The second resin composition preferably contains an inorganic filler.This makes it possible to obtain a prepreg 10 having high mechanicalstrength while having a reduced thickness (e.g., 35 μm or less). Inaddition, it is also possible to allow the prepreg 10 to have lowerthermal expansivity.

Examples of the inorganic filler include talc, alumina, glass, silica,mica, aluminum hydroxide, magnesium hydroxide, and the like. Among theseinorganic fillers, the silica is preferably used. From the viewpoint ofexcellent low thermal expansivity, molten silica (especially, sphericalmolten silica) is preferably used.

The inorganic filler (that is, the particles thereof) may have a crushedshape or a spherical shape, but a shape of the inorganic filler isappropriately selected according to its purpose of use. For example, inorder to impregnate the sheet-shaped base member 1 with the second resincomposition reliably, it is preferred that a melt viscosity of thesecond resin composition is reduced. In this case, spherical silica ispreferably used as the inorganic filler.

An average particle size of the inorganic filler is not particularlylimited to a specific value, but is preferably in the range of 0.01 to5.0 μm, and more preferably in the range of 0.2 to 2.0 μm.

If the average particle size of the inorganic filler is less than theabove lower limit value, there is a case that the melt viscosity of thesecond resin composition becomes high depending on an amount of theinorganic filler contained in the second resin composition, and thelike, thereby affecting workability during manufacture of the prepreg10.

On the other hand, if the average particle size of the inorganic fillerexceeds the above upper limit value, there is a case that a phenomenonsuch as sedimentation of the inorganic filler in a varnish for forming asecond resin layer occurs.

In this regard, it is to be noted that the average particle size of theinorganic filler can be measured by, for example, a particle sizedistribution analyzer (“LA-500” produced by HORIBA).

As the inorganic filler, spherical silica (especially, spherical moltensilica) is preferably used. An average particle size of the sphericalmolten silica is preferably 5.0 μm or less, and more preferably in therange of 0.01 to 2.0 μm. By using such spherical silica as the inorganicfiller, it is possible to improve a filling factor (packing density) ofthe inorganic filler within the second resin layer

In the case where the inorganic filler is used, an amount of theinorganic filler contained in the second resin composition is notparticularly limited to a specific value, but is preferably in the rangeof 40 to 80 wt %, more preferably in the range of 50 to 70 wt %, andeven more preferably in the range of 60 to 70 wt % with respect to atotal weight of the second resin composition.

By setting the amount of the inorganic filler contained in the secondresin composition to a value within the above range, it is possible togive especially excellent low thermal expansivity and lowwater-absorption properties to the second resin layer 3.

In the case where the cyanate resin (especially, novolak type cyanateresin) is used as the curable resin, epoxy resin (which containssubstantially no halogen atom) is preferably used in combination withthe cyanate resin. Examples of the epoxy resin include phenol novolaktype epoxy resin, bisphenol type epoxy resin, naphthalene type epoxyresin, arylalkylene type epoxy resin, and the like.

Among these epoxy resins, the arylalkylene type epoxy resin ispreferably used. By using such epoxy resin, it is possible for the curedsecond resin layer 3 (obtained substrate) to have improved solder heatresistance after moisture absorption and flame retardancy.

The arylalkylene type epoxy resin is epoxy resin having one or morearylalkylene groups in one repeating unit. Examples of such arylalkylenetype epoxy resin include xylylene type epoxy resin, biphenyldimethylenetype epoxy resin, and the like. Among these arylalkylene type epoxyresins, the biphenyldimethylene type epoxy resin is preferably used.

The biphenyldimethylene type epoxy resin can be represented by, forexample, the following formula (II).

wherein n is any integer.

An average number of repeating units n of the biphenyldimethylene typeepoxy resin represented by the above formula (II) is not particularlylimited to a specific value, but is preferably in the range of 1 to 10,and more preferably in the range of 2 to 5.

If the average number of repeating units n is less than the above lowerlimit value, the biphenyldimethylene type epoxy resin tends to becrystallized, thereby reducing solubility of the biphenyldimethylenetype epoxy resin in general purpose-solvents. As a result, there is acase that it becomes difficult to handle a varnish for forming a secondresin layer.

On the other hand, if the average number of repeating units n exceedsthe above upper limit value, there is a case that flowability of thesecond resin composition in a molten state is lowered, thereby causingdefective molding of the prepreg 10, and the like.

In the case where a combination of the epoxy resin and the cyanate resinis used as the curable resin, an amount of the epoxy resin contained inthe second resin composition is not particularly limited to a specificvalue, but is preferably in the range of 1 to 55 wt %, and morepreferably in the range of 2 to 40 wt % with respect to a total weightof the second resin composition.

If the amount of the epoxy resin contained in the second resincomposition is less than the above lower limit value, there is a casethat reactivity of the cyanate resin is lowered or moisture resistanceof the prepreg 10 is lowered.

On the other hand, if the amount of the epoxy resin contained in thesecond resin composition exceeds the above upper limit value, there is acase that heat resistance of the prepreg 10 is lowered depending on akind of the epoxy resin used, and the like.

A weight average molecular weight of the epoxy resin is not particularlylimited to a specific value, but is preferably in the range of 500 to20,000, and more preferably in the range of 800 to 15,000.

If the weight average molecular weight of the epoxy resin is less thanthe above lower limit value, there is a case that the prepreg 10 becomestacky depending on ambient temperature, and the like.

On the other hand, if the weight average molecular weight of the epoxyresin exceeds the above upper limit value, there is a case that itbecomes difficult to impregnate the sheet-shaped base member 1 (corelayer 11) with the second resin composition in the manufacturing processof the prepreg 10 and therefore a prepreg 10 having uniform thicknessand uniform quality cannot be obtained.

In this regard, it is to be noted that the weight average molecularweight of the epoxy resin can be measured using, for example, a GPC (gelpermeation chromatography).

Further, in the case where the cyanate resin (especially, novolak typecyanate resin) is used as the thermosetting resin, phenolic resin ispreferably used in combination with the cyanate resin. Examples of thephenolic resin include novolak type phenolic resin, resol type phenolicresin, arylalkylene type phenolic resin, and the like.

Among these phenolic resins, the arylalkylene type phenolic resin ispreferably used. By using such phenolic resin, it is possible to allowthe cured second resin layer 3 (obtained substrate) to have improvedsolder heat resistance after moisture absorption.

Examples of the arylalkylene type phenolic resin include xylylene typephenolic resin, biphenyldimethylene type phenolic resin, and the like.The biphenyldimethylene type phenolic resin can be represented by, forexample, the following formula (III).

wherein n is any integer.

An average number of repeating units n of the biphenyldimethylene typephenolic resin represented by the above formula (III) is notparticularly limited to a specific value, but is preferably in the rangeof 1 to 12, and more preferably in the range of 2 to 8.

If the average number of repeating units n of the biphenyldimethylenetype phenolic resin is less than the above lower limit value, there is acase that heat resistance of the second resin layer 3 is lowereddepending on an amount of the biphenyldimethylene type phenolic resincontained in the second resin composition, and the like.

On the other hand, if the average number of repeating units n of thebiphenyldimethylene type phenolic resin exceeds the above upper limitvalue, there is a case that mutual solubility between thebiphenyldimethylene type phenolic resin and another resin (curableresin) tends to be lowered, thereby lowering workability duringmanufacture of the prepreg 10.

By using the cyanate resin (especially, novolak type cyanate resin) incombination with the arylalkylene type phenolic resin, it is possible tocontrol crosslink density of the cured second resin composition, therebyimproving adhesiveness between a circuit wiring portion (that is, ametal constituting the circuit wiring portion) and the cured secondresin layer 3 (cured second resin composition).

In the case where a combination of the phenolic resin and the cyanateresin is used as the curable resin, an amount of the phenolic resincontained in the second resin composition is not particularly limited toa specific value, but is preferably in the range of 1 to 55 wt %, andmore preferably in the range of 5 to 40 wt % with respect to a totalweight of the second resin composition.

If the amount of the phenolic resin contained in the second resincomposition is less than the above lower limit value, there is a casethat heat resistance of the second resin layer 3 is lowered depending ona kind of the phenolic resin used, and the like.

On the other hand, if the amount of the phenolic resin contained in thesecond resin composition exceeds the above upper limit value, there is acase that low thermal expansivity of the second resin layer 3 isimpaired depending on a kind of the phenolic resin used, and the like.

A weight average molecular weight of the phenolic resin is notparticularly limited to a specific value, but is preferably in the rangeof 400 to 18,000, and more preferably in the range of 500 to 15,000.

If the weight average molecular weight of the phenolic resin is lessthan the above lower limit value, there is a case that the prepreg 10becomes tacky depending on ambient temperature, and the like.

On the other hand, if the weight average molecular weight of thephenolic resin exceeds the above upper limit value, there is a case thatit becomes difficult to impregnate the sheet-shaped base member 1 (corelayer 11) with the second resin composition in the manufacturing processof the prepreg 10 and therefore a prepreg 10 having uniform thicknessand uniform quality cannot be obtained.

In this regard, it is to be noted that the weight average molecularweight of the phenolic resin can be measured using, for example, a GPC(gel permeation chromatography).

Further, by using the cyanate resin (especially, novolak type cyanateresin), the phenolic resin (arylalkylene type phenolic resin,especially, biphenyldimethylene type phenolic resin), and the epoxyresin (arylalkylene type epoxy resin, especially, biphenyldimethylenetype epoxy resin) in combination, it is possible to obtain a prepreg 10capable of manufacturing a substrate (especially, circuit substrate)having especially excellent dimensional stability.

The second resin composition preferably contains a coupling agent. Thecoupling agent has a function of improving wettability of an interfacebetween the curable resin and the inorganic filler.

Therefore, by adding such a coupling agent to the second resincomposition, it is possible to uniformly fix the curable resin and theinorganic filler to the sheet-shaped base member 1. This makes itpossible to improve heat resistance of the second resin layer 3,especially, solder heat resistance after moisture absorption of thecured second resin layer 3.

The coupling agent is not particularly limited to a specific type aslong as it is generally used. Examples of such a coupling agent includean epoxy silane coupling agent, a cationic silane coupling agent, anamino silane coupling agent, a titanate-based coupling agent, a siliconeoil type coupling agent, and the like, and one or more of these curingagents are preferably used.

By using such a coupling agent, it is possible to enhance thewettability of the interface between the curable resin and the inorganicfiller, thereby further improving the heat resistance of the secondresin layer 3.

In the case where the coupling agent is used, an amount of the couplingagent contained in the second resin composition is not particularlylimited to a specific value, because it can be set to a desired valuedepending on a surface area of the inorganic filler used.

However it is preferably in the range of 0.05 to 3 parts by weight, andmore preferably in the range of 0.1 to 2 parts by weight with respect to100 parts by weight of the inorganic filler.

If the amount of the coupling agent contained in the second resincomposition is less than the above lower limit value, there is a casethat it is impossible to sufficiently cover the surface of the inorganicfiller with the coupling agent depending on a kind of the coupling agentused, a kind, shape or size of the inorganic filler used, and the like,thereby reducing the effect of improving the heat resistance of thesecond resin layer 3.

On the other hand, if the amount of the coupling agent contained in thesecond resin composition exceeds the above upper limit value, there is acase that the coupling agent affects a curing reaction of the curableresin depending on a kind of the curable resin used, and the like,thereby reducing bending strength of the cured second resin layer 3(obtained substrate).

If necessary, the second resin composition may contain a curingaccelerator. As the curing accelerator, a well-known one can be used.Examples of such a curing accelerator include: organometallic salt suchas zinc naphthenate, cobalt naphthenate, tin octylate, cobalt octylate,cobalt (II) bisacetylacetonate, or cobalt (III) triacetylacetonate;tertiary amine such as triethylamine, tributylamine, ordiazabicyclo[2,2,2]octane; imidazole such as 2-phenyl-4-methylimidazole,2-ethyl-4-ethylimidazole, 2-phenyl-4-methyl imidazole,2-phenyl-4-methyl-5-hydroxyimidazole, or2-phenyl-4,5-dihydroxyimidazole; a phenol compound such as phenol,bisphenol A, or nonylphenol; organic acid such as acetic acid, benzoicacid, salicylic acid, or paratoluenesulfonic acid; a mixture thereof;and the like.

In the case where the curing accelerator is used, an amount of thecuring accelerator contained in the second resin composition is notparticularly limited to a specific value, but is preferably in the rangeof 0.05 to 5 wt %, and more preferably in the range of 0.2 to 2 wt %with respect to a total weight of the second resin composition.

If the amount of the curing accelerator contained in the second resincomposition is less than the above lower limit value, there is a casethat an effect of accelerating a curing reaction of the curable resincannot be sufficiently exhibited depending on a kind of the curableresin used, and the like.

On the other hand, if the amount of the curing accelerator contained inthe second resin composition exceeds the above upper limit value, thereis a case that storage stability of the prepreg 10 is reduced dependingon a kind of the curing accelerator used, and the like.

In this regard, it is to be noted that each of the first and secondresin compositions may contain thermoplastic resin to be used incombination with the curable resin. Examples of the thermoplastic resininclude phenoxy resin, polyimide resin, polyamideimide resin,polyphenylene oxide resin, polyethersulfone resin, and the like.

Further, if necessary, the second resin composition may further containone or more additives in addition to the above-described components.Examples of such additives include a pigment, an antioxidant, and thelike.

A thickness of the second resin layer 3 is not particularly limited to aspecific value, because it can be set to a desired value depending on athickness of a circuit wiring portion (inner layer circuit) to beembedded into the second resin layer 3. However, a thickness representedby “t2” in the following formula 1) is preferably in the range of 0.1 to5 μm, and more preferably in the range of 1 to 3 μm.

By setting the thickness “t2” to a value within the above range, it ispossible to obtain a prepreg 10 having especially excellentembeddability of the circuit wiring portion while having a small totalthickness (namely, it is possible to obtain a prepreg 10 havingespecially excellent moldability while having a small total thickness).B1=t1×(1−S/100)+t2  Formula 1)

In this formula 1), as shown in FIG. 1, a thickness of the second resinlayer 3 is represented by “B1 (μm)”, and as shown in FIG. 2, a thicknessof a circuit wiring portion (inner layer circuit) 4 is represented by“t1 (μm)”, a residual copper ratio of the circuit wiring portion 4 isrepresented by “S (%)”, and a thickness from an upper surface 41 of thecircuit wiring portion 4 to an upper surface 31 of the second resinlayer 3 is represented by “t2”.

In this regard, it is to be noted that in FIG. 1, the thickness of thesecond resin layer 3 “B1” is larger than that of the first resin layer 2“B2” (that is, B1>B2), but according to the present embodiment, “B1” maybe equal to “B2” (that is, B1=B2) or “B1” may be smaller than “B2” (thatis, B1<B2).

A thermal expansion coefficient of the second resin layer 3 at a planedirection (X-Y direction) thereof is not particularly limited to aspecific value, but is preferably 20 ppm or less, and more preferably inthe range of 5 to 16 ppm.

By setting the thermal expansion coefficient of the second resin layer 3in a plane direction (X-Y direction) thereof to a value within the aboverange, it is possible to allow the prepreg 10 to have especiallyexcellent connection reliability and therefore to obtain a substratewhich offers excellent reliability in the case where a semiconductorelement or the like is mounted thereon.

The above-described prepreg 10 can be manufactured by, for example, thefollowing method.

First, the first resin composition is applied or supplied on a carrierfilm (that is, a first sheet member) in the form of a layer to prepare acarrier member 2 a, and the second resin composition is applied orsupplied on a carrier film (that is, a second sheet member) in the formof a layer to prepare a carrier member 3 a.

Next, the carrier member 2 a and the carrier member 3 a are laminated on(overlapped with) the sheet-shaped base member 1 (or the core layer 11),and they are joined together to obtain a laminate.

Next, if necessary, the carrier films (first and second sheet members)are removed from the laminate to thereby obtain a prepreg 10 includingtwo resin layers formed of resin compositions having differentconstitutions on both surfaces of the sheet-shaped base member 1.

Hereinbelow, a method for preparing carrier members 2 a and 3 a eachhaving a structure in which a resin composition is applied on a carrierfilm in advance, laminating the carrier members 2 a and 3 a on thesheet-shaped base member 1, and removing the carrier films will bespecifically described based on FIG. 3.

FIG. 3 is a diagram showing one example of a process for manufacturing aprepreg according to the present invention.

First, a sheet-shaped base member 1 (or a core layer 11), a carriermember 2 a having a resin layer (first resin layer 2) formed of thefirst resin composition described above, and a carrier member 3 a havinga resin layer (second resin layer 3) formed of the second resincomposition described above are prepared.

The carrier member 2 a can be obtained by, for example, applying avarnish containing the first resin composition (that is, a varnish forforming a first resin layer) on a carrier film. Further, the carriermember 3 a can be obtained by, for example, applying a varnishcontaining the second resin composition (that is, a varnish for forminga second resin layer) on a carrier film.

Next, the carrier members 2 a and 3 a are laminated with thesheet-shaped base member 1 using a vacuum laminator 8 so that two resinlayers (first resin composition and second resin composition) makecontact with both surfaces of the sheet-shaped base member 1 underreduced pressure, respectively, and the carrier members 2 a and 3 a andthe sheet-shaped base member 1 are joined together using laminationrolls 81 to obtain a laminate.

In this regard, it is to be noted that the joining together of thesheet-shaped base member 1 and the carrier members 2 a and 3 a may alsobe carried out under normal pressure, but is preferably carried outunder reduced pressure.

In the case where the joining together of the sheet-shaped base member 1and the carrier members 2 a and 3 a is carried out under reducedpressure, even if non-filled portions, which are not filled by the firstresin composition and the second resin composition, would be produced inthe sheet-shaped base member 1 or at a joint (interface) between thesheet-shaped base member 1 and each of the carrier members 2 a and 3 a,the non-filled portions can exist as decompression voids orsubstantially vacuum voids.

Since such decompression voids or vacuum voids can be removed easily andreliably during the step of removing bubbles (e.g., heat treatment)which will be described later, a prepreg 10 to be finally obtained canbe well molded without such voids (bubbles) or the like.

Such joining together of the sheet-shaped base member 1 and the carriermembers 2 a and 3 a under reduced pressure can also be carried out usingother apparatus such as a vacuum box.

After the completion of joining together of the sheet-shaped base member1 and the carrier members 2 a and 3 a, the laminate is subjected to aheat treatment using a hot-air drier 9 at a temperature equal to orhigher than melting points of the resin compositions constituting thecarrier members 2 a and 3 a.

Specifically, it is preferred that the heat treatment is carried out ata temperature of a melting point or higher, wherein the melting point isa higher melting point than the melting point of the first resincomposition and the melting point of the second resin composition.

By doing so, even in the case where the decompression voids or the likeare produced in the step of joining the sheet-shaped base member 1 andthe carrier members 2 a and 3 a together under reduced pressure, it ispossible to remove the decompression voids or the like from thelaminate. Namely, it is possible to remove bubbles from the laminate bythe heat treatment.

The heat treatment can also be carried out by another method using, forexample, an infrared heater, a heating roller, a flat plate type hotpress machine or the like.

In this regard, it is to be noted that removal of the bubbles from thelaminate can also be carried out by, for example, applying ultrasonicvibration to the laminate, instead of the heat treatment. Alternatively,the removal of the bubbles from the laminate may also be carried out bya combination of the heat treatment and the application of theultrasonic vibration.

Next, in the case where the carrier film of each of the carrier members2 a and 3 a is formed from a resin sheet, the resin sheets are removedfrom the laminate to obtain a prepreg 10.

In this case, it is preferred that a surface of each of the carrierfilms on which the resin composition is to be applied is subjected to arelease treatment. By doing so, it is possible to peel off the carrierfilms from the resin layers (remove the carrier films from the laminate)more easily and reliably.

As described above, the prepreg 10 is adapted to be used in a state thata conductor layer is provided on the upper surface of the first resinlayer 2. Therefore, in the case where the carrier film (first sheetmember) of the carrier member 2 a is formed of a conductive material,the carrier film may be used as the conductor layer without removing itfrom the laminate.

By doing so, it is possible to eliminate necessity to additionallyprovide a conductor layer on the upper surface of the prepreg 10 (firstresin layer 2). This makes it possible to reduce a manufacturing cost ofa substrate (multilayer substrate) and therefore to reduce amanufacturing cost of a semiconductor device.

In this regard, it is to be noted that by using the method describedabove, it is possible to easily obtain a prepreg 10 even in the casewhere a sheet-shaped base member 1 having a thickness of 25 μm or lessis used.

Meanwhile, according to a conventional method for manufacturing aprepreg (that is, a method in which a sheet-shaped base member isimmersed into and impregnated with a resin varnish using a coatingmachine usually used, and then is dried), it is difficult to obtain aprepreg which uses a sheet-shaped base member having a thickness of 30μm or less.

More specifically, when such a thin sheet-shaped base member having manyfine openings is passed through many transfer rolls after immersionthereof into a thermosetting resin (resin material), or an amount of aresin material to be impregnated into the sheet-shaped base member isadjusted, stress is applied to the sheet-shaped base member. As aresult, there is a case that the openings of the sheet-shaped basemember are enlarged or the sheet-shaped base member breaks when wound updue to the applied stress.

On the other hand, according to the method of the present inventiondescribed above, it is possible to allow the sheet-shaped base member 1to support the carrier members 2 a and 3 a even in the case where it hasa relatively small thickness (e.g., 25 μm or less). This makes itpossible to easily obtain not only a prepreg 10 having a usual thicknessbut also a prepreg 10 having a relatively small thickness of 35 μm orless.

As a result, a thickness of the prepreg 10 provided between upper andlower circuit wiring portions (conductive circuit layers) in a moldedsubstrate can be made 35 μM or less. By reducing the thickness of theprepreg 10 provided between the conductive circuit layers to 35 μm orless, it is also possible to reduce a thickness of a finally obtainedsubstrate.

Alternatively, such a prepreg 10 can also be obtained by, for example,applying a low viscosity varnish for forming a first resin layer on onesurface of a sheet-shaped base member 1, drying the varnish to form afirst resin layer 2, applying a varnish for forming a second resin layeron the other surface of the sheet-shaped base member 1, and drying thevarnish to form a second resin layer 3.

A thermal expansion coefficient of such a prepreg 10 in a planedirection thereof is not particularly limited to a specific value, butis preferably 16 ppm or less, more preferably 12 ppm or less, and evenmore preferably in the range of 5 to 10 ppm.

By setting the thermal expansion coefficient of the prepreg 10 in aplane direction thereof to a value within the above range, it ispossible to allow an obtained substrate to have improved resistance tocrack that is likely to be caused by repeated thermal shocks.

The thermal expansion coefficient of the prepreg 10 in a plane directionthereof can be evaluated by heating the prepreg 10 with a TMA instrument(produced by TA Instrument) at a temperature rise rate of 10° C./min.

A thickness of the prepreg 10 according to the present embodiment is notparticularly limited to a specific value, but is preferably in the rangeof 20 to 80 μm, and more preferably in the range of 30 to 60 μm. Bysetting the thickness of the prepreg 10 to a value within the aboverange, it is possible to finally obtain a very thin substrate.

In this regard, it is to be noted that in the prepreg 10 according tothe present embodiment, the sheet-shaped base member 1 may be locatedclose to one surface of the prepreg 10 in a thickness direction thereofas in the case of a prepreg according to a second embodiment (which willbe described later).

Namely, a thickness of the first resin layer 2 may be different fromthat of the second resin layer 3. For example, in the case where circuitwiring portions are embedded into both of the first resin layer 2 andthe second resin layer 3, an amount of a resin composition for formingeach of the resin layers 2 and 3 can be controlled depending on acircuit wiring portion to be embedded into (joined to) the resin layerof the prepreg 10.

In particular, in the case where a conductor layer (that is, a circuitwiring portion) is formed on the first resin layer 2, it is preferredthat the thickness of the first resin layer 2 is set to a value smallerthan that of the second resin layer 3. By doing so, it is possible toenhance rigidity of the first resin layer 2 and therefore to form theconductor layer more easily and reliably.

Second Embodiment

Hereinbelow, another preferred embodiment (second embodiment) of theprepreg according to the present invention will be described based onthe accompanying drawings.

In this regard, it is to be noted that the prepreg according to thesecond embodiment will be described by focusing differences between thefirst and second embodiments, and a description of the overlappingpoints will be omitted.

FIGS. 4( a), 4(b) and 5 are sectional views each showing one example(second embodiment) of the prepreg according to the present invention.In this regard, it is to be noted that a top and a bottom of each ofFIGS. 4( a) and 4(b) are in a reversed relation with respect to those ofFIG. 5.

A prepreg 10 according to the second embodiment is different from theprepreg 10 according to the first embodiment in the following points.Namely, in the prepreg 10 according to the second embodiment, aconstitution of a first resin composition constituting a first resinlayer 2 is identical with that of a second resin compositionconstituting a second resin layer 3, and a thickness of the first resinlayer 2 is different from that of the second resin layer 3.

In other words, as shown in FIGS. 4( a) and 4(b), each prepreg 10according to the second embodiment has a structure in which the sameresin composition is supported on both surfaces of a sheet-shaped basemember (fiber base member) 1, and the sheet-shaped base member 1 (or thecore layer 11) is located close to one surface of the prepreg 10 in athickness direction thereof.

The phrase “the sheet-shaped base member 1 (or the core layer 11) islocated close to one surface of the prepreg 10 in a thickness directionthereof” used herein means a state as shown in FIGS. 4( a) and 4(b),where a center of each sheet-shaped base member 1 is dislocated from acenter line A-A of the prepreg 10 in a thickness direction thereof.

As shown in FIG. 4( a), the sheet-shaped base member 1 is provided inthe prepreg 10 in a state that the lower surface (lower surface in FIG.4( a)) of the sheet-shaped base member 1 is located close to the lowersurface (lower surface in FIG. 4( a)) of the prepreg 10.

On the other hand, in the prepreg 10 shown in FIG. 4( b), thesheet-shaped base member 1 is provided between a center line A-A of theprepreg 10 and the lower surface (lower surface in FIG. 4( b)) of theprepreg 10. In this regard, it is to be noted that the sheet-shaped basemember 1 may be located at a position indicated by the center line A-Aof the prepreg 10.

Further, a state that the sheet-shaped base member 1 is located close toone surface of the prepreg 10 in a thickness direction thereof may be astate shown in either FIG. 4( a) or FIG. 4( b), but the state shown inFIG. 4( b), that is, a state shown in FIG. 5 is more preferable.

More specifically, as shown in FIG. 4( b), when a thickness of a thickresin layer (that is, the second resin layer 3) is defined as “B1 (μm)”and a thickness of a thin resin layer (that is, the first resin layer 2)is defined as “B2 (μm)”, a ratio of B2 to B1 (that is, B2/B1) ispreferably larger than 0 but less than 1 (that is, 0<B2/B1<1).

Further, the ratio B2/B1 between the thickness B1 of the second resinlayer 3 and the thickness B2 of the first resin layer 2 is notparticularly limited to a specific value.

However, the ratio B2/B1 is preferably 0.5 or less, and more preferablyin the range of 0.2 to 0.4. By setting the ratio B2/B1 to a value withinthe above range, it is possible to prevent the sheet-shaped base member1 from becoming wavy and therefore to further improve flatness of theprepreg 10.

Further, the thickness B2 is not particularly limited to a specificvalue. However, from the viewpoint of giving plating adhesiveness to asurface (upper surface in FIG. 5) of the prepreg 10, the thickness B2 ispreferably in the range of 5 to 15 μm, and more preferably in the rangeof 8 to 10 μm.

By setting the thickness B2 to a value within the above range, it ispossible to reliably give plating adhesiveness to the upper surface (onesurface) of the prepreg 10.

According to the second embodiment, the sheet-shaped base member 1 ismade to have a thickness of 25 μm or less to thereby reduce thethickness of the prepreg 10. More specifically, the thickness of thesheet-shaped base member 1 is preferably 20 μm or less, and morepreferably in the range of 10 to 15 μm.

By setting the thickness of the sheet-shaped base member 1 to a valuewithin the above range, it is possible to reduce a thickness of anobtained substrate (which will be described later) while maintainingmechanical strength of the substrate.

In addition, it is also possible to obtain a prepreg 10 having excellentworkability for establishing interlayer connection and therefore toallow an obtained substrate to have excellent reliability of interlayerconnection.

As the sheet-shaped base member (fiber base member) 1, the same one asused in the first embodiment can be used. Further, as the resincomposition, the same one as used in the second resin compositionaccording to the first embodiment can be used. Furthermore, the prepreg10 according to the second embodiment can be manufactured in the samemanner as in the first embodiment.

However, in the case of the second embodiment, the first resincomposition and the second resin composition are made to have the sameconstitution (composition), and the thickness of the resin layer of thecarrier member 2 a is made smaller than that of the resin layer of thecarrier member 3 a.

In this way, it is possible to obtain a prepreg 10, in which asheet-shaped base member 1 having a relatively small thickness (e.g., 25μm or less) is located close to one surface of the prepreg 10 in athickness direction thereof.

By setting the thicknesses of each of the resin layers of the carriermembers 2 a and 3 a to a desired value, it is also possible to easilyreduce the thickness of the prepreg 10 to 35 μm or less.

By reducing the thickness of the prepreg 10 to 35 μm or less, it ispossible to reduce a thickness of an obtained substrate, even in thecase where the substrate is a multilayer substrate. This also makes itpossible to reduce a thickness of a finally obtained semiconductordevice.

In this regard, it is to be noted that the thickness of the prepreg 10according to the present embodiment is not particularly limited to aspecific value, but is preferably 30 μm or less, and more preferably inthe range of 20 to 25 μm.

By setting the thickness of the prepreg 10 according to the presentembodiment to a value within the above range, it is possible to allow anobtained substrate to have a small thickness even in the case where thesubstrate is a multilayer substrate having 6 or more layers. This alsomakes it possible to reduce a thickness of a finally obtainedsemiconductor device.

Meanwhile, according to a conventional prepreg manufacturing method, thesame resin composition is applied on both surfaces of a sheet-shapedbase member to obtain a prepreg.

More specifically, the conventional prepreg includes a sheet-shaped basemember, and two resin layers provided on both surfaces thereof,respectively, the resin layers each having the same thickness andconstituted of the same resin composition.

However, in the case where two different circuit wiring portions(especially, two circuit wiring portions having different residualcopper ratios) are respectively embedded into the two resin layers ofthe conventional prepreg in a manufacturing process of a substrate,there is a case that the resin composition constituting the prepreg issqueezed out of the substrate or the resin composition cannotsufficiently fill gaps in the circuit wiring portion.

This is because the conventional prepreg cannot be suitably used respondto a situation where an amount of the resin composition required to fillthe gaps in the circuit wiring portion is different between the tworesin layers.

On the other hand, in the prepreg 10 according to the presentembodiment, the sheet-shaped base member 1 is located close to onesurface of the prepreg 10 in a thickness direction thereof.

Therefore, it is possible to design a prepreg 10 having a necessary andsufficient amount of a resin composition for filling gaps in each of twocircuit wiring portions to be built up on both surfaces of the prepreg10 (that is, two circuit wiring portions to be embedded into both resinlayers).

In addition, it is also possible to manufacture a thin prepreg 10 havinga thickness of 35 μm or less. Further, by locating the sheet-shaped basemember 1 at a position close to one side surface of the prepreg 10 in athickness direction thereof, it is also possible to reduce a thicknessof a finally obtained semiconductor device.

This is because the prepreg 10 is simply thin and the amount of theresin composition of the prepreg 10 can be controlled depending on aresidual copper ratio of a circuit wiring portion to be embeddedthereinto, and therefore it becomes possible to avoid formation of resinlayer containing an unnecessary amount of the resin composition.

In this regard, it is to be noted that in the prepreg 10 according tothe present embodiment, the constitution of the resin composition (firstresin layer 2) provided on the one surface of the sheet-shaped basemember 1 may be different from that of the resin composition (secondresin layer 3) provided on the other surface of the sheet-shaped basemember 1 as is the case with the prepreg 10 according to the firstembodiment.

The phrase “the constitution of the resin composition provided on theone surface of the sheet-shaped base member 1 may be different from thatof a resin composition provided on the other surface of the sheet-shapedbase member 1” herein used has the same meaning as described above withreference to the first embodiment.

By allowing the prepreg 10 to have two resin compositions havingdifferent constitutions on both surface sides thereof, it is possible todesign resin layers so as to have according to desired characteristics(properties). This makes it possible to extend a range of choices ofresin compositions to be used.

For example, a resin layer, into which a circuit wiring portion (innerlayer circuit) is to be embedded, can be formed of a flexible resincomposition in view of embeddability, and a resin layer provided on theopposite side of the above resin layer can be formed of a rigid resincomposition in view of rigidity.

In this way, it is possible to give different functions to two resinlayers provided on both surfaces of the prepreg 10.

Hereinbelow, a substrate having the prepreg 10 described above and asemiconductor device having such a substrate will be described.

As shown in FIG. 6, a substrate 100 includes a core substrate 101, threeprepregs 10 a, 10 b and 10 c provided at an upper side of the coresubstrate 101, and three prepregs 10 d, 10 e and 10 f provided at alower side of the core substrate 101.

Predetermined circuit wiring portions (circuit wiring patterns) 4 areprovided between the core substrate 101 and the prepreg 10 c, the coresubstrate 101 and the prepreg 10 d, the prepreg 10 a and the prepreg 10b, the prepreg 10 b and the prepreg 10 c, the prepreg 10 d and theprepreg 10 e, and the prepreg 10 e and the prepreg 10 f. Further, padportions 5 are provided on an upper surface of the prepreg 10 a and alower surface of the prepreg 10 f.

It is preferred that at least one of these prepregs 10 a to 10 f(preferably, all of these prepregs 10 a to 10 f) is formed from theabove-described prepreg 10 (e.g., the prepreg 10 having a thickness of35 μm or less). By doing so, a thickness of the substrate (circuitsubstrate) 100 can be made thin.

These circuit wiring portions 4 are electrically connected by filled viaportions 6 provided in the prepregs 10 a to 10 f and the core substrate101 so as to pass through each of them.

Case I: each of the prepregs 10 a to 10 f constituting the substrate 100is formed from the prepreg 10 according to the first embodiment.

In this case, a constitution of the first resin composition constitutingthe first resin layers 2 (upper resin layers of the prepregs 10 a to 10c and lower resin layers of the prepregs 10 d to 10 f in FIG. 6), onwhich the circuit wiring portions (patterned conductor layers) 4 areformed, is different from that of the second resin compositionconstituting the second resin layers 3 each provided on the oppositeside of the first resin layer 2 in each of the prepregs 10 a to 10 f.

The first resin composition constituting the first resin layers 2 isdesigned to have improved adhesiveness to a conductor layer to beprovided on the first resin layer 2 of each of the prepregs 10 a to 10f. This makes it possible for the first resin layers 2 to have goodadhesiveness to the circuit wiring portions 4.

On the other hand, the second resin composition constituting the secondresin layers 3 is designed to have improved embeddability of the circuitwiring portion 4 and low thermal expansivity.

Further, by reducing a thickness of the first resin layer 2 of each ofthe prepregs 10 a to 10 f to a minimum value required to improveadhesiveness to the circuit wiring portion 4 and by reducing a thicknessof the second resin layer 3 of each of the prepregs 10 a to 10 f to aminimum value required to embed the circuit wiring portion 4 thereinto,it is also possible to reduce a total thickness of the substrate 100.

Case II: each of the prepregs 10 a to 10 f constituting the substrate100 is formed from the prepreg 10 according to the second embodiment.

In this case, since in each of the prepregs 10 a to 10 f thesheet-shaped base member 1 is located close to the one surface of theprepreg in a thickness direction thereof, it is possible to provideflexibility in the structure of the limitations such as a height(thickness) of each circuit wiring portion (inner layer conductorcircuit) 4 to be embedded thereinto, and the like.

This makes it possible to increase a degree of freedom of design of thecircuit wiring portion 4, and therefore it is possible to form thecircuit wiring portion 4 easily. In addition, it is also possible todesign the prepreg 10 so that each of the second resin layers 3 has alarger thickness and this makes it possible for the circuit wiringportion 4 to be easily embedded into the second resin layer 3.

For these reasons, a risk of developing a problem caused by contactbetween the circuit wiring portion 4 and the sheet-shaped base member 1can be reduced.

As shown in FIG. 5, the circuit wiring portion 4 is embedded into theresin composition of the second resin layer 3 of the prepreg 10 (e.g.,prepreg 10 c shown in FIGS. 6 and 7) which has a larger thickness thanthe first resin layer 2.

In other words, gaps (space portions) between wires constituting thecircuit wiring portion 4 are filled with a part of the resin compositionof the second resin layer 3.

In this regard, when a total thickness of the prepreg 10 is defined as“T0 (μm)” as shown in FIG. 4 and a height (thickness) of the circuitwiring portion 4 is defined as “t1 (μm)” as shown in FIG. 5, adifference between T0 and t1 (especially, t3) is not particularlylimited to a specific value, but is preferably 35 μm or less, and morepreferably in the range of 10 to 30 μm.

By setting the difference between T0 and t1 to a value within the aboverange, it is possible to sufficiently keep (ensure) insulationreliability of the substrate 100 even in the case where the substrate100 is formed to have a small thickness.

Now, as shown in FIG. 5, the t3 corresponds to a thickness from an uppersurface 41 of the circuit wiring portion 4 to an upper surface 21 of theprepreg 10 (that is, an upper surface of the first resin layer 2).

As shown in FIGS. 4 and 5, when a thickness of a thicker resin layer(second resin layer 3) is defined as “B1 (μm)”, a thickness of a thinresin layer (first resin layer 2) is defined as “B2 (μm)”, a thicknessof the circuit wiring portion 4 is defined as “t1 (μm)”, a residualcopper ratio of the circuit wiring portion 4 is defined as “S (%)”, anda thickness from the upper surface 41 of the circuit wiring portion 4 tothe sheet-shaped base member 1 (that is, an upper surface 31 of thesecond resin layer 3) is defined as “t2 (μm)”, B2 and B1 preferablysatisfy a relation of B2<B1 and B1=t2+t1×(1−S/100).

In this regard, the thickness t2 is not particularly limited to aspecific value, but is preferably in the range of 0 to 15 μm. In thecase where there is a risk that insulation between the circuit wiringportion 4 and the sheet-shaped base member 1 is reduced so as to causepossible contact therebetween, the thickness t2 is preferably set to bea value in the range of 3 to 15 μm.

On the other hand, from the viewpoint of further reducing the thicknessof the substrate 100, the thickness t2 is preferably set to a value inthe range of 0 to 5 μm.

Further, from the viewpoint of achieving both of the high insulationreliability and the thickness reduction, the thickness t2 is preferablyin the range of 3 to 5 μm. By setting the thickness t2 to a value withinthe above range, it is possible to give excellent embeddability of thecircuit wiring portion 4 and high insulation reliability to the secondresin layer 3.

Furthermore, as shown in FIG. 7, a semiconductor device 200 can beobtained by mounting a semiconductor element 7 on the substrate 100 insuch a manner that bumps 71 of the semiconductor element 7 are connectedto the pad portions 5 of the substrate 5.

By adjusting the thickness of the first resin layer 2 and the thicknessof the second resin layer 3 of each of the prepregs 10 a to 10 f tooptimum values, it is possible to optimize the total thickness of thesubstrate 100.

As a result, it is possible to obtain a semiconductor device 200 havinga necessary and minimum thickness for satisfying required properties.

Although the substrate 100 having 6 prepregs 10 a to 10 f has beendescribed above based on FIGS. 6 and 7, the substrate according to thepresent invention is not limited thereto. The present invention can bealso applied to a substrate having 3, 4, or 5 prepregs or a multilayersubstrate (multilayer wiring substrate) having 7, 8, or more prepregs.

Further, the substrate 100 according to the present invention may useboth the prepreg 10 according to the first embodiment and the prepreg 10according to the second embodiment, and may further use a conventionalprepreg together with the prepreg 10 according to the first embodimentand the prepreg 10 according to the second embodiment.

In this regard, it is to be noted that in the case where two or moreprepregs 10 according to the second embodiment are used, each of themmay have the sheet-shaped base member 1 located in a different positionin a thickness direction of the prepreg 10.

EXAMPLES

Hereinbelow, the present invention will be described in detail based onthe following Examples and Comparative Examples, but the presentinvention is not limited to these Examples. First, Examples of theprepreg according to the present invention will be described.

Example 1 1. Preparation of Varnish for Forming First Resin Layer

24 wt % of cyanate resin having a weight average molecular weight ofabout 2,600 (“Primaset PT-30” produced by LONZA Japan) as thermosettingresin, 24 wt % of biphenyldimethylene type epoxy resin having an epoxyequivalent of 275 (“NC-3000” produced by Nippon Kayaku Co., Ltd.) asepoxy resin, 11.8 wt % of phenoxy resin being a copolymer of bisphenol Atype epoxy resin and bisphenol F type epoxy resin, having an epoxy groupat each end, and having a weight average molecular weight of 60,000(“EP-4275” produced by Japan Epoxy Resins Co., Ltd.) as phenoxy resin,and 0.2 wt % of an imidazole compound (“2-phenyl-4,5-dihydroxymethylimidazole” produced by Shikoku Chemicals Corporation) as a curingcatalyst were dissolved into methyl ethyl ketone to obtain a mixture.

Further, 39.8 wt % of spherical molten silica having an average particlesize of 0.5 μm (“SO-25H” produced by Admatechs Co., Ltd.) as aninorganic filler and 0.2 wt % of an epoxy silane type coupling agent(“A-187” produced by Nippon Unicar Co., Ltd.) were added into themixture, and it was stirred using a high speed stirring machine for 60minutes. In this way, a varnish for forming a first resin layer having asolid content of 60 wt % was prepared.

2. Preparation of Varnish for Forming Second Resin Layer

15 wt % of novolak type cyanate resin having an weight average molecularweight of about 2,600 (“Primaset PT-30” produced by LONZA Japan) asthermosetting resin, 8.7 wt % of biphenyldimethylene type epoxy resinhaving an epoxy equivalent of 275 (“NC-3000” produced by Nippon KayakuCo., Ltd.) as epoxy resin, and 6.3 wt % of biphenyldimethylene typephenolic resin having a hydroxyl equivalent of 200 (“GPH-65” produced byNippon Kayaku Co., Ltd.) as phenolic resin were dissolved into methylethyl ketone to obtain a mixture.

Further, 69.7 wt % of spherical molten silica-having an average particlesize of 0.5 μm (“SO-25H” produced by Admatechs Co., Ltd.) as aninorganic filler and 0.3 wt % of an epoxy silane type coupling agent(“A-187” produced by Nippon Unicar Co., Ltd.) were added into themixture, and it was stirred using a high speed stirring machine for 60minutes. In this way, a varnish for forming a second resin layer havinga solid content of 60 wt % was prepared.

3. Preparation of Carrier Member

A polyethylene terephthalate film (“SFB-38” produced by MitsubishiPolyester Film Corporation) having a thickness of 38 μm and a width of480 mm was prepared as a carrier film, and the varnish for forming afirst resin layer prepared above was applied on the carrier film using acomma coater and was then dried using a drier at 170° C. for 3 minutes.

In this way, a carrier member 2 a was obtained. In this regard, it is tobe noted that in the thus obtained carrier member 2 a, a resin layer(that is, a resin layer eventually used as a first resin layer) having athickness of 9 μm and a width of 410 mm was centrally located on thecarrier film in a width direction thereof.

A carrier member 3 a was obtained in the same manner as in the case ofthe carrier member 2 a except that the varnish for forming a first resinlayer was replaced with the varnish for forming a second resin layer andan amount thereof was changed.

In this regard, it is to be noted that in the thus obtained carriermember 3 a, a resin layer (that is, a resin layer eventually used as asecond resin layer) having a thickness of 14 μm and a width of 360 mmwas centrally located on the carrier film in a width direction thereof.

4. Manufacture of Prepreg

A glass woven cloth (a cloth type thereof was #1015, a width thereof was360 mm, a thickness thereof was 15 μm, and a basis weight thereof was 17g/m²) was prepared as a sheet-shaped base member, and a prepreg havingthe glass woven cloth was manufactured using a vacuum laminator and ahot air drier shown in FIG. 3.

More specifically, the carrier member 2 a was laminated on one surfaceof the glass woven cloth and the carrier member 3 a was laminated on theother surface of the glass woven cloth so that the carrier members 2 aand 3 a are centrally located in a width direction of the glass wovencloth, and then the carrier member 2 a, the carrier member 3 a, and theglass woven cloth were joined together using laminating rolls at 80° C.under reduced pressure of 1330 Pa to obtain a laminate.

In this regard, it is to be noted that, in an inside area of thelaminate that lay within the width of the glass woven cloth, the resinlayer of the carrier member 2 a was joined to the one surface of theglass woven cloth and the resin layer of the carrier member 3 a wasjoined to the other surface of the glass woven cloth, and in an outsidearea of the laminate that did not lie within the width of the glasswoven cloth, the resin layer of the carrier member 2 a and the resinlayer of the carrier member 3 a were joined to each other.

Next, the thus obtained laminate was passed through a hot air drier keptat 120° C. for 2 minutes using a horizontal conveyor so that thelaminate was subjected to a heat treatment without applying pressure.

Thereafter, the two carrier films were peeled off from the resin layersand removed from the laminate to thereby obtain a prepreg having athickness of 30 μm (a thickness of the first resin layer was 5 μm, athickness of the glass woven cloth was 15 μm and a thickness of thesecond resin layer was 10 μm).

Example 2

A prepreg was obtained in the same manner as in the Example 1 exceptthat the varnish for forming a first resin layer was replaced with oneprepared in the following manner. In this Example 2, a varnish forforming a first resin layer was prepared without using the cyanate resinas the thermosetting resin.

Namely, 24 wt % of biphenyldimethylene type epoxy resin having an epoxyequivalent of 275 (“NC-3000” produced by Nippon Kayaku Co., Ltd.) and17.5 wt % of liquid bisphenol type epoxy resin (“830S” produced byDAINIPPON INK AND CHEMICALS, INC.) as epoxy resins, 18 wt % of phenoxyresin being a copolymer containing bisphenol S skeletons (chemicalstructures), having an epoxy group at each end, and having a weightaverage molecular weight of 30,000 (“YX-8100” produced by Japan EpoxyResins Co., Ltd.) as phenoxy resin, and 0.2 wt % of an imidazolecompound (“2-phenyl-4,5-dihydroxymethyl imidazole” produced by ShikokuChemicals Corporation) as a curing catalyst were dissolved in methylethyl ketone to obtain a mixture.

Further, 39.8 wt % of spherical molten silica having an average particlesize of 0.5 μm (“SO-25H” produced by Admatechs Co., Ltd.) as aninorganic filler and 0.2 wt % of an epoxy silane type coupling agent(“A-187” produced by Nippon Unicar Co., Ltd.) were added into themixture, and it was stirred using a high speed stirring machine for 60minutes. In this way, a varnish for forming a first resin layer having asolid content of 60 wt % was prepared.

In this regard, it is to be noted that the thus obtained prepreg had athickness of 30 μm (a thickness of the first resin layer was 5 μm, athickness of the glass woven cloth was 15 μm and a thickness of thesecond resin layer was 10 μm).

Example 3

A prepreg was obtained in the same manner as in the Example 1 exceptthat the varnish for forming a second resin layer was replaced with oneprepared in the following manner.

17.5 wt % of biphenyldimethylene type epoxy resin having an epoxyequivalent of 275 (“NC-3000” produced by Nippon Kayaku Co., Ltd.) asepoxy resin and 12 wt % of biphenyldimethylene type phenolic resinhaving a hydroxyl equivalent of 200 (“GPH-65” produced by Nippon KayakuCo., Ltd.) as phenolic resin as thermosetting resins, 0.5 wt % ofimidazole (“2P4 MHZ” produced by Shikoku Chemicals Corporation), and anepoxy silane type coupling agent (“A-187” produced by Nippon Unicar Co.,Ltd.) as a coupling agent in an amount of 0.3 part by weight per 100parts by weight of total inorganic fillers (which will be describedlater) were dissolved into methyl ethyl ketone at room temperature toobtain a mixture.

Further, 20 wt % of spherical molten silica having an average particlesize of 0.3 μm (“SFP-10X” produced by Denki Kagaku Kogyo K.K.) and 50 wt% of spherical molten silica having an average particle size of 1.5 μm(“SO-32R” produced by Admatechs Co., Ltd.) as inorganic fillers wereadded into the mixture, and it was stirred using a high speed stirringmachine for 10 minutes. In this way, a varnish for forming a secondresin layer was prepared.

In this regard, it is to be noted that the thus obtained prepreg had athickness of 30 μm (a thickness of the first resin layer was 5 μm, athickness of the glass woven cloth was 15 μm and a thickness of thesecond resin layer was 10 μm).

Example 4

A prepreg was obtained in the same manner as in the Example 1 exceptthat the thickness of the resin layer of the carrier member 2 a waschanged to 14 μm and the thickness of the resin layer of the carriermember 3 a was changed to 14 μm.

In this regard, it is to be noted that the thus obtained prepreg had athickness of 35 μm (a thickness of the first resin layer was 10 μm, athickness of the glass woven cloth was 15 μm and a thickness of thesecond resin layer was 10 μm).

Example 5

A prepreg was obtained in the same manner as in the Example 1 exceptthat the sheet-shaped base member and the carrier members 2 a and 3 awere changed in the following manner.

The sheet-shaped base member was changed to a glass woven cloth (a clothtype thereof was #1037, a thickness thereof was 24 μm, and a basisweight thereof was 24 g/m²).

Further, the thickness of the resin layer of the carrier member 2 a waschanged to 12 μm and the thickness of the resin layer of the carriermember 3 a was changed to 18 μm.

In this regard, it is to be noted that the thus obtained prepreg had athickness of 40 μm (a thickness of the first resin layer was 5 μm, athickness of the glass woven cloth was 24 μm and a thickness of thesecond resin layer was 11 μm).

Example 6

A prepreg was obtained in the same manner as in the Example 1 exceptthat the sheet-shaped base member and the carrier members 2 a and 3 awere changed in the following manner.

The sheet-shaped base member was changed to a glass woven cloth (a clothtype thereof was #1080, a thickness thereof was 42 μm, and a basisweight thereof was 48 g/m²).

Further, the thickness of the resin layer of the carrier member 2 a waschanged to 20 μm and the thickness of the resin layer of the carriermember 3 a was changed to 22 μm.

In this regard, it is to be noted that the thus obtained prepreg had athickness of 60 μm (a thickness of the first resin layer was 8 μm, athickness of the glass woven cloth was 42 μm and a thickness of thesecond resin layer was 10 μm).

Example 7

A prepreg was obtained in the same manner as in the Example 1 exceptthat the varnish for forming a second resin layer was replaced with thevarnish for forming a first resin layer prepared in the Example 1.Namely, a constitution of the first resin composition and a constitutionof the second resin composition were the same.

In this regard, it is to be noted that the thus obtained prepreg had athickness of 30 μm (a thickness of the first resin layer was 5 μm, athickness of the glass woven cloth was 15 μm and a thickness of thesecond resin layer was 10 μm).

Example 8

A prepreg was obtained in the same manner as in the Example 1 exceptthat the varnish for forming a first resin layer was replaced with thevarnish for forming a second resin layer prepared in the Example 1.Namely, a constitution of the first resin composition and a constitutionof the second resin composition were the same.

In this regard, it is to be noted that the thus obtained prepreg had athickness of 30 μm (a thickness of the first resin layer was 5 μm, athickness of the glass woven cloth was 15 μm and a thickness of thesecond resin layer was 10 μm).

Example 9 1. Preparation of Varnish for Forming Resin Layer

15 wt % of novolak type cyanate resin having a weight average molecularweight of about 2,600 (“Primaset PT-30” produced by LONZA Japan) asthermosetting resin, 8 wt % of biphenyldimethylene type epoxy resinhaving an epoxy equivalent of 275 (“NC-3000P” produced by Nippon KayakuCo., Ltd.) as epoxy resin, 7 wt % of biphenyldimethylene type phenolicresin having a hydroxyl equivalent of 203 (“MEH-7851-S” produced byMeiwa Plastic Industries, Ltd.) as phenolic resin, and an epoxy silanetype coupling agent (“A-187” produced by Nippon Unicar Co., Ltd.) as acoupling agent in an amount of 0.3 part by weight per 100 parts byweight of total inorganic fillers (which will be described later) weredissolved into methyl ethyl ketone at room temperature to obtain amixture.

Further, 20 wt % of spherical molten silica having an average particlesize of 0.3 μm (“SFP-10X” produced by Denki Kagaku Kogyo K.K.) and 50 wt% of spherical molten silica having an average particle size of 1.5 μm(“SO-32R” produced by Admatechs Co., Ltd.) as inorganic fillers wereadded into the mixture, and it was stirred using a high speed stirringmachine for 10 minutes. In this way, a varnish for forming a resin layerwas prepared.

2. Preparation of Carrier Member

A polyethylene terephthalate film (“SFB-38” produced by MitsubishiPolyester Film Corporation) having a thickness of 38 μm and a width of480 mm was prepared as a carrier film, and the varnish for forming aresin layer prepared above was applied on the carrier film using a commacoater and was then dried using a drier at 170° C. for 3 minutes.

In this way, a carrier member 2 a was obtained. In this regard, it is tobe noted that in the thus obtained carrier member 2 a, a resin layer(that is, a resin layer eventually used as a first resin layer) having athickness of 8 μm and a width of 360 mm was centrally located on thecarrier film in a width direction thereof.

A carrier member 3 a was obtained in the same manner as in the case ofthe carrier member 2 a except that an amount of the varnish applied onthe carrier film was changed.

In this regard, it is to be noted that in the thus obtained carriermember 3 a, a resin layer (that is, a resin layer eventually used as asecond resin layer) having a thickness of 15 μm and a width of 410 mmwas centrally located on the carrier film in a width direction thereof.

3. Manufacture of Prepreg

A glass woven cloth (a cloth type thereof was #1015, a width thereof was360 mm, a thickness thereof was 15 μm, and a basis weight thereof was 17g/m²) was prepared as a sheet-shaped base member, and a prepreg usingthe glass woven cloth was manufactured using a vacuum laminator and ahot air drier shown in FIG. 3.

More specifically, the carrier member 2 a was laminated on one surfaceof the glass woven cloth and the carrier member 3 a was laminated on theother surface of the glass woven cloth so that the carrier members 2 aand 3 a are centrally located in a width direction of the glass wovencloth, and then the carrier member 2 a, the carrier member 3 a, and theglass woven cloth were joined together using laminating rolls at 80° C.under reduced pressure of 750 Torr to obtain a laminate.

In this regard, it is to be noted that, in an inside area of thelaminate which lay within the width of the glass woven cloth, the resinlayer of the carrier member 2 a was joined to the one surface of theglass woven cloth and the resin layer of the carrier member 3 a wasjoined to the other surface of the glass woven cloth, and in an outsidearea of the laminate which did not lie within the width of the glasswoven cloth, the resin layer of the carrier member 2 a and the resinlayer of the carrier member 3 a were joined to each other.

Next, the thus obtained laminate was passed through a hot air drier keptat 120° C. for 2 minutes using a horizontal conveyor so that thelaminate was subjected to a heat treatment without applying pressure.

Thereafter, the two carrier films were peeled off from the resin layersand removed from the laminate to thereby obtain a prepreg having athickness of 30 μm (a thickness of the first resin layer was 4 μm, athickness of the glass woven cloth was 15 μm and a thickness of thesecond resin layer was 11 μm).

Example 10

A prepreg was obtained in the same manner as in the Example 9 exceptthat the thickness of the resin layer of the carrier member 2 a waschanged to 8 μm and the thickness of the resin layer of the carriermember 3 a was changed to 20 μm.

In this regard, it is to be noted that the thus obtained prepreg had athickness of 35 μm (a thickness of the first resin layer was 4 μm, athickness of the glass woven cloth was 15 μm and a thickness of thesecond resin layer was 16 μm).

Example 11

A prepreg was obtained in the same manner as in the Example 9 exceptthat the sheet-shaped base member and the carrier members 2 a and 3 awere changed in the following manner.

The sheet-shaped base member was changed to a glass woven cloth (a clothtype thereof was #1037, a thickness thereof was 24 μm, and a basisweight thereof was 24 g/m²).

Further, the thickness of the resin layer of the carrier member 2 a waschanged to 11 μm and the thickness of the resin layer of the carriermember 3 a was changed to 20 μm.

In this regard, it is to be noted that in the thus obtained prepreg hada thickness of 40 μm (a thickness of the first resin layer was 4 μm, athickness of the glass woven cloth was 24 μm and a thickness of thesecond resin layer was 12 μm).

Example 12

A prepreg was obtained in the same manner as in the Example 9 exceptthat the varnish for forming a resin layer was replaced with oneprepared in the following manner.

100 parts by weight of epoxy resin (“Ep5048” produced by Japan EpoxyResins Co., Ltd.) as thermosetting resin, 2 parts by weight of a curingagent (dicyandiamide), and 0.1 part by weight of a curing accelerator(2-ethyl-4-methyl imidazole) were dissolved into 100 parts by weight ofmethyl cellosolve to thereby obtain a varnish for forming a resin layer.

In this regard, it is to be noted that the thus obtained prepreg had athickness of 35 μm (a thickness of the first resin layer was 4 μm, athickness of the glass woven cloth was 15 μm and a thickness of thesecond resin layer was 16 μm).

Example 13

A prepreg was obtained in the same manner as in the Example 9 exceptthat the carrier members 2 a and 3 a were changed in the followingmanner.

The thickness of the resin layer of the carrier member 2 a was changedto 8 μm and the thickness of the resin layer of the carrier member 3 awas changed to 25 μm.

In this regard, it is to be noted that the thus obtained prepreg had athickness of 40 μm (a thickness of the first resin layer was 4 μm, athickness of the glass woven cloth was 15 μm and a thickness of thesecond resin layer was 21 μm).

Comparative Example 1

A prepreg was obtained in the same manner as in the Example 9 exceptthat the sheet-shaped base member and the carrier members 2 a and 3 awere changed in the following manner.

The sheet-shaped base member was changed to a glass woven cloth (a clothtype thereof was #1080, a thickness thereof was 55 μm, and a basisweight thereof was 47 g/m²).

Further, the thickness of the resin layer of the carrier member 2 a waschanged to 25 μm and the thickness of the resin layer of the carriermember 3 a was changed to 25 μm.

In this regard, it is to be noted that in the thus obtained prepreg hada thickness of 75 μm (a thickness of the first resin layer was 10 μm, athickness of the glass woven cloth was 55 μm and a thickness of thesecond resin layer was 10 μm).

Comparative Example 2

A prepreg was obtained in the same manner as in the Example 9 exceptthat the sheet-shaped base member and the carrier members 2 a and 3 awere changed in the following manner.

The sheet-shaped base member was changed to a glass woven cloth (a clothtype thereof was #1037, a thickness thereof was 24 μm, and a basisweight thereof was 24 g/m²).

Further, the thickness of the resin layer of the carrier member 2 a waschanged to 16 μm and the thickness of the resin layer of the carriermember 3 a was changed to 16 μm.

In this regard, it is to be noted that in the thus obtained prepreg hada thickness of 40 μm (a thickness of the first resin layer was 8 μm, athickness of the glass woven cloth was 24 μm and a thickness of thesecond resin layer was 8 μm).

The prepregs obtained in the Examples 1 to 13 and the ComparativeExamples 1 and 2 were evaluated in the following manner.

1. Ratio of Thickness of First Resin Layer and Thickness of Second ResinLayer

The thickness of each resin layer of the prepreg was measured in a crosssection of the prepreg.

2. Thermal Expansion Coefficient of Prepreg in Plane Direction

A thermal expansion coefficient of the prepreg in a plane directionthereof was measured using a TMA instrument (produced by TA Instrument)at a temperature rise rate of 10° C./min.

3. Elastic Modulus of Prepreg

An elastic modulus of the prepreg was measured by DMA (“DMA 983”produced by TA Instrument) in a resonant shear mode at a temperaturerise rate of 5° C./min.

These evaluation items and evaluation results are shown in Table 1.

TABLE 1 Ratio Thermal of Thick- Expansion Elastic T0 B1 B2 nessesCoefficient Modulus [μm] [μm] [μm] (B2/B1) [ppm] [MPa] Example 1 30 10 50.50 11 24 Example 2 30 10 5 0.50 12 22 Example 3 30 10 5 0.50 15 20Example 4 35 10 10 1.00 12 23 Example 5 40 11 5 0.45 11 24 Example 6 6010 8 0.80 12 25 Example 7 30 10 5 0.50 15 22 Example 8 30 10 5 0.50 8 25Example 9 30 11 4 0.36 8 25 Example 10 35 16 4 0.25 10 24 Example 11 4012 4 0.33 8 25 Example 12 35 16 4 0.25 12 22 Example 13 40 21 4 0.19 1024 Comparative 75 10 10 1.00 8 26 Example 1 Comparative 40 8 8 1.00 8 25Example 2

As can be seen from Table 1, each of the prepregs of the Examples 1 to 3and 5 to 13 had the first resin layer and the second resin layer havingdifferent thicknesses, and thus in each of these prepregs, thesheet-shaped base member is was located close to one surface of theprepreg in a thickness direction thereof.

Therefore, each of the prepregs could have a resin layer whose thicknesscan vary depending on a residual copper ratio of a circuit wiringportion to be embedded thereinto, a circuit thickness (circuit height),and the like.

Further, all of the prepregs of the Examples 1 to 13 have a low thermalexpansion coefficient and a high elastic modulus. From these results, itcan be expected that substrates using such prepregs will have excellentconnection reliability.

I. Measurement of Thickness and Evaluation of Moldability and PlatingAdhesiveness

10 multilayer substrates (substrates) were manufactured using theprepregs obtained in each of the Examples to 13 and Comparative Examples1 and 2, and then 10 semiconductor devices were manufactured using thethus obtained substrates. Each multilayer substrate and eachsemiconductor device were manufactured as follows.

First, a core substrate 101, on which a circuit wiring portion 4 havinga comb shape was provided, was prepared. In this regard, it is to benoted that gaps between wires constituting the circuit wiring portion 4had a width of 50 μm, and the circuit wiring portion 4 had apredetermined circuit thickness and a residual copper ratio of 50%.

Next, the prepreg was laminated on the core substrate 101 so as to makecontact with circuit wiring portion 4, and a copper foil as an outermostlayer was further laminated on the prepreg to obtain a laminate. Andthen the laminate was heated and pressure-molded under conditions of 3MPa, 200° C. and 90 minutes to thereby obtain a multilayer substrate.

Thereafter, the copper foil (conductor layer), which was the outermostlayer and had a thickness of 12 μm, was formed into a circuit, and thena semiconductor element was mounted on the circuit to thereby obtain asemiconductor device.

The thus obtained multilayer substrates using the prepregs obtained inthe Examples and Comparative Examples and the semiconductor devicesusing these substrates were evaluated in the following points.

1. Thickness t3 (Interlayer Thickness)

A thickness t3 (that is, the thickness from the upper surface 41 of thecircuit wiring portion 4 to the upper surface 21 of the first resinlayer 2) of each multilayer substrate was measured by observing a crosssection of the substrate.

2. Thickness t2

A thickness t2 (that is, the thickness from the upper surface 41 of thecircuit wiring portion 4 to the upper surface 31 of the second resinlayer 3) of each multilayer substrate was measured by observing thecross section of the substrate.

In this regard, it is to be noted that a difference of the measuredvalue of the interlayer thickness t3 and a designed value thereof wascalculated and shown in Table 2.

3. Embeddability

A cross section of the circuit wiring portion 4 in the substrate wasobserved with a microscope, and then embeddability of the resin layer ofthe prepreg was evaluated according to the following four criteria.

A: All of the substrates had excellent embeddability.

B: The circuit wiring portion 4 was made contact with the glass wovencloth partially, but which did not cause any problem in practical use ofthe substrate.

C: The circuit wiring portion 4 was made contact with the glass wovencloth partially, which made it impossible to practically use thesubstrate.

D: The resin layer was not embedded into the gaps between the wiresconstituting the circuit wiring portion 4 sufficiently, and thereforevoids or the like were observed within the gaps.

4. Plating Adhesiveness

Plated copper peel strength of the copper foil to the first resin layer(upper resin layer) was measured for each prepreg, and then based on themeasured value, plating adhesiveness of the first resin layer of theprepreg was evaluated according to the following four criteria.

A: 0.6 kN/m or more

B: 0.5 kN/m or more but less than 0.6 kN/m

C: 0.4 kN/m or more but less than 0.5 kN/m

D: less than 0.4 kN/m

II. Evaluation of Insulation Reliability

In order to test insulation reliability, 10 multilayer substrates(four-layer printed wiring boards) each provided with circuit wiringportions 4 having a comb shape as inner and outer layers thereof weremanufactured using the prepregs obtained in each of the Examples andComparative Examples. In this regard, it is to be noted that gapsbetween wires constituting the circuit wiring portion 4 had a width of50 μm.

Insulation resistance of each multilayer substrate was measured using anautomatic ultra-insulation resistance meter (produced by ADVANTEST).Then, a direct current of 50 V was applied to the printed wiring boardfor 96 hours in an atmosphere of PCT-130° C./85%, and then theinsulation resistance of the multilayer substrate was measured.

Based on the measured values of the insulation resistance, theinsulation reliability of the multilayer substrate was evaluatedaccording to the following four criteria. In this regard, it is to benoted that the insulation resistance was measured under the conditionthat a voltage of 100 V was applied for 1 minute.

A: 1×10⁹Ω or more

B: 1×10⁸Ω or more but less than 1×10⁹Ω

C: 1×10⁷Ω or more but less than 1×10⁸Ω

D: less than 1×10⁷Ω

III. Evaluation of Connection Reliability (Temperature Cycling (TC)Test)

10 daisy chain type semiconductor devices for evaluation use weremanufactured by connecting a semiconductor element having 300 bumps to amultilayer substrate manufactured using the prepreg obtained in each ofthe Examples and Comparative Examples via the bumps.

Electrical continuity of each semiconductor device was checked, and theneach semiconductor device was subjected to a temperature cycling (TC)test by repeating a cycle consisting of 10-minute cooling at −50° C. and10-minute heating at 125° C.

Every 100 cycles during the TC test, a number of the semiconductordevices in which disconnection occurred was counted.

Based on the number of the semiconductor devices in which disconnectionoccurred, connection reliability of the semiconductor device wasevaluated according to the following four criteria.

A: The number of the semiconductor devices in which disconnectionoccurred was 0 even after completion of 1000 cycles of the TC test.

B: The number of the semiconductor devices in which disconnectionoccurred was 0 after completion of 800 cycles of the TC test, but was 5or more after completion of 1000 cycles of the TC test.

C: The number of the semiconductor devices in which disconnectionoccurred was 0 after completion of 600 cycles of the TC test, but was 5or more after completion of 800 cycles of the TC test and was 10 aftercompletion of 1000 cycles of the TC test.

D: The number of the semiconductor devices in which disconnectionoccurred was 5 or more after completion of 600 cycles of the TC test,but reached 10 before completion of 800 cycles of the TC test.

The measurement results are shown in Table 2, and evaluation items andevaluation results are shown in Table 3.

TABLE 2 Thickness of t1 t2 t3 Substrate [μm] [μm] [μm] t3 - DesignedValue [μm] Example 1 12 4 24 0 146 Example 2 12 5 25 +1 148 Example 3 124 24 0 146 Example 4 12 4 28 −1 154 Example 5 12 5 34 0 166 Example 6 125 55 +1 208 Example 7 12 7 27 +3 152 Example 8 12 4 22 −2 142 Example 918 2 20 0 150 Example 10 18 7 27 +1 164 Example 11 18 3 31 0 172 Example12 18 7 26 0 162 Example 13 18 12 30 −1 170 Comparative 18 1 64 −2 238Example 1 Comparative 18 0 31 — 172 Example 2 (Defective Molding)

TABLE 3 Plating Insulation Connection Embeddability AdhesivenessReliability Reliability Example 1 A A A A Example 2 A A A A Example 3 AA A A Example 4 A A A A Example 5 A A A A Example 6 A A A A Example 7 DA A B Example 8 B B-C A A Example 9 B A A A Example 10 A A A A Example11 B A A A Example 12 A A A A Example 13 A A A A Comparative C A D DExample 1 Comparative D A D D Example 2

As can be seen from Table 3, especially, the prepregs of the Examples 1to 6 and 9 to 13 had excellent embeddability and plating adhesiveness.In a conventional prepreg, such results were difficult to achievesimultaneously.

Further, since the multilayer substrates using the prepregs obtained inthe Examples 1 to 6 and 9 to 13 each having a second resin layer formedof a resin composition having excellent embeddability and low thermalexpansivity, they exhibited excellent insulation reliability.

In addition, the semiconductor devices using these multilayer substratesexhibited excellent connection reliability.

Further, as can be seen from Table 2, the multilayer substrate using theprepreg obtained in the Example 6 had a thickness slightly larger than200 μm, but other multilayer substrates using the prepregs obtained inthe Examples 1 to 5 and 7 to 13 had small thicknesses of 200 μm or less.

Therefore, these results show that a multilayer substrate having a smallthickness could be obtained according to the present invention. Further,in all of the multilayer substrates using the prepregs obtained in theExamples 1 to 13, squeezing out of the resin composition was notobserved.

Further, it was confirmed that all of the semiconductor devices usingthe prepregs obtained in the Examples 1 to 13 could operate normallywithout any practical problems.

On the other hand, all of the multilayer substrates using the prepregsobtained in the Comparative Examples 1 and had poor insulationreliability, and therefore the semiconductor devices using thesemultilayer substrates had poor connection reliability and could notoperate normally.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a prepregwhich can meet a demand for thickness reduction, and which has first andsecond resin layers having different applications, functions,capabilities, or properties, or which allows an amount of a resincomposition in each of the first and second resin layers to be setappropriately depending on a circuit wiring portion to be embedded intothe second resin layer.

For example, by appropriately selecting a combination of a first resincomposition for the first resin layer and a second resin composition forthe second resin layer, it is possible to provide a prepreg whose onesurface (first resin layer) has excellent plating adhesiveness and whoseother surface (second resin layer) has excellent embeddability.

Further, in the prepreg according to the present invention, asheet-shaped base member can be located close to one surface of theprepreg in a thickness direction thereof depending on a residual copperratio of a circuit wiring portion to be embedded thereinto, a circuitthickness (circuit height) thereof, and the like.

This makes it possible to obtain a prepreg which includes a resin layerhaving a necessary and sufficient amount of a resin composition forfilling gaps in a circuit wiring portion to be embedded into the resinlayer.

Further, according to the present invention, it is also possible toprovide a method for manufacturing the prepreg of the present invention.By using the method according to the present invention, it is possibleto easily manufacture the prepreg of the present invention at a lowcost.

Furthermore, according to the present invention, it is also possible toprovide a substrate using the prepreg of the present invention and asemiconductor device using such a substrate. The substrate and thesemiconductor device according to the present invention can have a smallthickness.

As a result, the substrate (especially, multilayer circuit substrate)using the prepreg of the present invention can have excellent insulationreliability, and the semiconductor device using such a substrate canhave excellent connection reliability.

For these reasons, the prepreg according to the present invention issuitable for manufacturing a multilayer circuit substrate and asemiconductor device which are required to have a higher density and asmaller thickness.

Thus, the present invention has industrial applicability.

1. A method for manufacturing a prepreg, comprising: preparing a corelayer, a first sheet member having one surface on which a first resincomposition is applied in the form of a layer, and a second sheet memberhaving one surface on which a second resin composition is applied in theform of a layer; laminating the core layer with the first sheet memberand the second sheet member so that the first resin composition and thesecond resin composition make contact with both surfaces of the corelayer, respectively, whereby the core layer, the first sheet member andthe second sheet member are joined together under reduced pressure withrespect to normal pressure in a vacuum laminate or vacuum box to obtaina laminate; and removing bubbles from the laminate.
 2. The method asclaimed in claim 1, wherein removing of the bubbles from the laminate iscarried out by a heat treatment.
 3. The method as claimed in claim 2,wherein the heat treatment is carried out at a temperature of a meltingpoint or higher, wherein the melting point is a higher melting pointthan a melting point of the first resin composition and a melting pointof the second resin composition.
 4. The method as claimed in claim 1,wherein the first sheet member is formed of a conductive material. 5.The method as claimed in claim 1, wherein each of the first sheet memberand the second member is formed from a resin sheet, and wherein themethod further comprises after removing the bubbles from the laminate,removing the resin sheets from the laminate.
 6. The method as claimed inclaim 5, wherein a surface of each of the resin sheets on which eachresin composition is applied is subjected to a release treatment.
 7. Themethod as claimed in claim 1, wherein the reduced pressure is in therange of 1330 to 99990 Pa.